Israeli air strikes on Gaza killed 15 Palestinians, including a top militant, medics said on Saturday, as militants fired 100 rockets into the Jewish state.

It was the deadliest violence between Israel and the Palestinians across the Gaza border in more than three years, prompting the United States and the European Union to urge both sides to restore calm.

But Palestinian militants vowed to avenge their dead and Israel threatened to hit back if its citizens came under renew rocket attacks from the coastal enclave.

Medics said three Palestinians were killed in air strikes on Saturday, one near the southern town of Rafah on the border with Egypt and two in Khan Yunis.

Saturday's deaths brought to 15 the total number of Palestinians killed since Friday, medics said, adding that at least 26 Palestinians were wounded, five seriously.

The army said more than 100 rockets and mortar rounds were fired into Israel from Gaza over the past 24 hours, including 27 which were intercepted by the Iron Dome anti-missile system.

Four people, three of them Thai labourers, were wounded inside Israel, media and Israeli medics said.

Residents interviewed on radio and television said they had been told to stay close to bomb shelters and that large public gatherings had been banned, leading to the cancellation of several football matches on Saturday.

Schools in southern Israel were due to remain closed on Sunday for security reasons.

The army said it attacked several targets inside Gaza including "a terrorist squad" planning to fire rockets.

It said the air raids were "in direct response to the rocket fire at Israeli communities in southern Israel."

One of the strikes killed the head of the Popular Resistance Committees, Zohair al-Qaisi, and fellow member Mahmud Hanani, the ultra-hardline militant group said.

The PRC threatened reprisals for Qaisi's death, while Al-Quds Brigades, the military wing of Islamic Jihad, said the air strikes also killed 10 of its members.

It was the deadly 24-hour period on the Gaza-Israel border since a devastating Israeli assault in December 2008-January 2009 aimed at halting Palestinian rocket attacks.

Thousands of mourners, many chanting calls for revenge and firing automatic weapons into the air, buried on Saturday 12 Palestinians and local officials said Israeli troops opened fire wounding four mourners.

The army had no immediate comment.

Defence Minister Ehud Barak said "the Israeli army will hit anyone planning to attack Israeli citizens," and that he expected the violence to continue another day or two.

Barak said Israel will continue to develop the capabilities of the Iron Dome system, while Prime Minister Benjamin Netanyahu said new batteries would be deployed to defend southern Israel.

Designed to intercept rockets and artillery shells fired from a range of between four and 70 kilometres (three and 45 miles), Iron Dome is part of an ambitious multi-layered defence programme to protect Israeli cities.

The Israeli military said Qaisi "was among the leaders who planned, funded and directed" a deadly cross-border attack into southern Israel from Egypt's Sinai peninsula last August that killed eight people.

The PRC militants killed on Friday night were also "planning a combined terror attack that was to take place via Sinai in the coming days," the military said.

Hamas, which rules Gaza, has maintained a tacit truce with Israel, but other Palestinian groups regularly fire rockets and mortars across the border, often sparking retaliatory air strikes.

The relatively small PRC is one of the most active.

"We are not committed to the truce; we will respond very strongly to this (Israeli) crime," Abu Ataya, a spokesman for the PRC's military wing, the Al-Nasser Salaheddin Brigades, told AFP.

Hamas also branded the killings a crime.

"The Al-Qassam Brigades mourn the martyr leader Zohair Qaisi and martyr Mahmud Hanani and confirm that their blood will not be wasted," the group's military wing said.

"The recent Zionist escalation... comes as a part of the destabilisation of a stable security situation in the Gaza Strip," the Hamas-run Gaza government's interior ministry said.

The PRC and Al-Aqsa Martyrs Brigades, an armed offshoot of Palestinian president Mahmud Abbas's Fatah movement, said they fired rockets into Israel on Friday.

The Palestinian Authority condemned Israel's retaliation, saying it would "escalate the circle of violence in the region."

The United States and European Union expressed similar concerns. "We call on both sides to make every effort to restore calm," said US State Department spokesman Victoria Nuland echoing an EU statement.

The Arab League accused Israel of carrying out a "massacre" and called for a tough stance from the international community against the Jewish state.

Gaza tensions since January 2011
Jerusalem (AFP) March 10, 2012 - After relative calm since Israel and Hamas entered a tacit truce last August, a new round of tit-for-tat fighting erupted on Friday after militants fired rockets into the Jewish state and the Israelis responded with an air strike that killed a militant chief.

Here are the main developments in tensions between Israel and the Palestinians since the beginning of last year:

JANUARY 2011

- 5: Israeli troops kill one Palestinian and wound another, saying they were trying to cross the border fence.

- 7: Militants wound four Israeli soldiers with gunshots and mortar fire.

- 11: Israeli warplanes kill one man and injure another in Gaza.

- 13: Hamas orders its security forces to ensure militant groups observe a truce on firing rockets at Israel a day after the factions agreed to comply.

- 17: A rocket hits southern Israel despite the promised truce.

- 18: A teenager is killed and two other people wounded as Israeli tanks carry out an operation in northern Gaza.

- 22: Israeli artillery fire kills a Palestinian and wounds two, Palestinian medics say in statements denied by the army.

FEBRUARY 2011

- 17: Three Palestinians are shot dead during clashes with the Israeli army.

- 23: Israeli tank fire kills one Palestinian fighter and wounds 10 other people in clashes, as militants fire the first rocket at the southern Israeli city of Beersheva since the Operation Cast Lead offensive against Gaza.

- 24: Prime Minister Benjamin Netanyahu warns Gaza militants not to "test" Israel, as fighter jets pounded targets across the coastal enclave.

- 27: A Palestinian is killed when an Israeli tank opens fire on a group of militants.

- 28: Israeli troops kill a Palestinian who was collecting gravel in what Israel says was an off-limits border zone.

MARCH 2011

- 16: An Israeli air strike kills two militants from the Ezzedine al-Qassam Brigades, the armed wing of Hamas after a mortar shell lands in Israel.

- 19: The Ezzedine al-Qassam Brigades, which had been observing a de facto truce since the end of Cast Lead, fire some 50 mortar rounds at Israel to avenge the deaths three days earlier.

- 20: Two Palestinian teenagers are shot dead near the security barrier as they were trying to sneak into Israel to find work, relatives say.

- 22: In what was the bloodiest day since the January 2009 end of Cast Lead, air strikes and tank attacks kill eight Palestinians -- four members of the military wing of Islamic Jihad, and four civilians who were playing football, including two children. Netanyahu expresses his regrets at the civilian deaths.

- 23: Gaza rocket and mortar fire on Israel continues, with the Al-Quds Brigades firing three Grad rockets and vowing to strike deep into Israel.

A package bomb explodes in Jerusalem, the first such attack since 2004, killing one person and wounding more than 30. No one claims responsibility.

Netanyahu promises to defend Israel with a "will of iron."

Hamas says it is determined to restore calm in Gaza.

- 24: Four Palestinians, including one militant, are wounded by air strikes on a day in which fire from Gaza continues to hit Israel.

- 26: Palestinian militant factions announce that they are committed to calming tensions if the Jewish state reciprocates.

- 27: Israeli air strike kills two militants from Islamic Jihad, which vows revenge for their deaths.

Israel deploys a first battery of its "Iron Dome" anti-missile system in Beersheva to defend the city against rocket attacks.

APRIL 2011

- 7: An anti-tank missile fired from Gaza hits a school bus in Israel fatally wounding a youngster. Israeli Defence Minister Ehud Barak orders the army to "react swiftly with all necessary means." In the ensuing three-day wave of Israeli reprisals and Palestinian counter-strikes 19 Palestinians were killed and 66 wounded.

- 10: Israel and Hamas halted hostilities.

AUGUST 2011

- 18: Gunmen ambush Israeli buses and cars on Route 12, which runs along the Egyptian border, 20 kilometres (12 miles) north of the Israeli Red Sea resort of Eilat, killing eight Israelis and wounding more than 25. Israel blames the Gaza-based Popular Resistance Committees militant group, which denies responsibility.

- 18-19: Israeli aerial reprisals on Gaza kill 15 Palestinians, including members and leaders of armed groups.

- 18-21: About 100 rockets and mortar rounds are fired into southern Israel, killing one Israeli.

- 21: Hamas announces that the main militant groups agree to an informal truce on condition that Israel stop attacking the Gaza Strip.

- 26: The truce finally takes hold after 26 Palestinians and one Israeli are killed

OCTOBER 2011

- 29-30: Israeli air strike kills five Palestinians about to fire rockets. Ten Palestinians and an Israeli are killed in 24 hours. After Egyptian intervention Gaza Palestinian factions agree to resume the truce.

DECEMBER 2011

- 9: The death of two Palestinian fighters in an Israeli air strike sparks another flareup of rocket fire and aerial retaliation in which two Palestinian civilians are killed.

MARCH 2012

- 9-10: Israeli air strikes on Gaza kill 14 Palestinians, including the Popular Resistance Committees chief, and wound 20. Militants fire at least 90 rockets and mortar rounds into Israel.