US Secretary of State John Kerry has strongly condemned Russia's pledge to sell an advanced missile system to Damascus, questioning Moscow's commitment to end the Syrian conflict, as concern grew for civilians trapped in the battle for a key Syrian town.

Speaking from Washington, Kerry warned that the planned delivery of S-300 air defence missiles to Damascus was "not helpful" as the US and Russia pressed on with their joint efforts to set up a peace conference, dubbed Geneva 2, to try to end the Syrian conflict.

Kerry said the delivery would have a "profoundly negative impact on the balance of interests and the stability of the region, and it does put Israel at risk".

It is "not helpful to have the S-300 transferred to the region while you are trying to organise this peace and create peace," he added, questioning whether Russia was fully committed to ending Syria's two-year-old conflict.

German Foreign Minister Guido Westerwelle, in Washington for talks with Kerry, also appealed to Russia to consider.

"I would like to make this absolutely clear. We tell our Russian colleagues, don't endanger the conference in Geneva," he said.

"The delivery of weapons to the Assad regime is totally wrong," he said.

In a television interview broadcast Thursday, Syrian President Bashar al-Assad appeared to imply that Russia had already started to deliver sophisticated S-300 missile systems under a contract with Syria.

Russia's Vedomosti and Kommersant newspapers said Moscow might not deliver the missiles this year, rejecting claims they had already arrived.

Russian news agency Interfax reported that Moscow could supply 10 ultra-modern MiG-29 fighter jets to Syria under a possible contract being discussed with Damascus.

Syrian troops and Hezbollah allies meanwhile pressed ahead with their assault on the strategic town of Qusayr as hundreds of rebels reportedly broke through army lines to join the battle.

The Syrian opposition said Friday that hundreds of rebel reinforcements, most of them close to the Muslim Brotherhood, had now reached Qusayr.

"Around 1,000 fighters from across Syria" had penetrated the town near the Lebanese border, the National Coalition's interim leader George Sabra told reporters in Istanbul.

"Hundreds" of rebels have broken through army lines near the village of Shamsinn, northeast of Qusayr, after losing 11 fighters, according to Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.

The Coalition has appealed for the rescue of 1,000 civilians wounded in Qusayr, which Assad's forces have been trying to retake in an all-out offensive since May 19.

Thousands of people who have fled the besieged town are in dire need of aid, the UN's refugee agency said, as its tally for Syrians who have escaped their war-torn nation topped 1.6 million.

UNHCR spokesman Dan McNorton told reporters that at least 3,500 people -- mostly women and children -- had made it to nearby Hasiya.

The agency was able "to witness the dire humanitarian situation of these displaced families", he said.

In Geneva, doctors from the Union of Syrian Medical Relief Organisations told AFP its members had seen "dozens of cases" of patients suffering from what they believe are chemical weapons attacks, mostly civilians.

The numbers of such cases seemed to be rising, said Tawfik Chamaa, a founding member of the UOSSM.

President Bashar al-Assad, meanwhile, said he was "very confident" of victory, in the interview with Hezbollah's Al-Manar television on Thursday.

Assad, whose forces are battling alongside fighters from Lebanon's Shiite movement Hezbollah to recapture Qusayr, said his regime would defeat the revolt which has raged since March 2011 at an estimated cost of more than 94,000 lives.

Syrian state television said troops and Hezbollah fighters captured the northern district of Arjun in Qusayr on Thursday, leaving rebels little chance to escape.

The EU on Friday formally waived the arms embargo against rebels, leaving members free from June 1 to decide at their discretion whether to supply carefully vetted weapons to the opposition.

But there was a joint commitment to refrain for the moment from supplying weapons for fear of endangering the Geneva 2 talks, with a review of that policy due "before August 1".

In New York, the UN Security Council added rebel Islamist group Al-Nusra Front to its global sanctions list because of its links to Al-Qaeda, making it subject to an international assets freeze and arms embargo.

On the ground, the Observatory reported that Syrian troops had killed three Westerners, including a US woman and a British man, both Muslims, near the border with Turkey on Wednesday.

Both Britain and the US confirmed that one of their nationals had been reported killed.

The Observatory also reported more than 30 prisoners killed in 10 days of clashes between rebels and loyalist forces at the main Aleppo prison, which holds around 4,000 inmates.

Assad implies missiles arrive as Syria peace bid stalls
Beirut (AFP) May 30, 2013 - Russia has sent Syria promised air defence missiles, President Bashar al-Assad implied in an interview to be aired Thursday, in a move aimed at deterring foreign intervention in the more than two-year conflict.

Moscow, the Assad regime's most powerful ally, announced this week it intends to honour its contract to supply Syria with the advanced S-300 missiles.

The opposition National Coalition, meeting in Istanbul, said it would not take part in a US-Russian peace initiative dubbed Geneva 2 "so long as the militias of Iran and Hezbollah keep up their invasion".

The declaration came as the Coalition appealed for the rescue of 1,000 citizens wounded in Qusayr, a town that elite regime forces backed by fighters from the Lebanese Shiite movement Hezbollah are battling to recapture from rebels.

The Assad interview is scheduled to be broadcast on Al-Manar, the channel of Hezbollah, his closest regional ally along with Shiite-ruled Iran, at 1800 GMT on Thursday.

In it, Assad, who belongs to the Alawite offshoot of Shiite Islam, implicitly acknowledged Russia has already delivered some of the promised S-300s.

Al-Manar said that when asked about the delivery of the surface-to-air missiles, Assad replied: "All the agreements with Russia will be honoured and some already have been recently."

Moscow has yet to confirm if it has already sent S-300s to Syria.

Israeli Defence Minister Moshe Yaalon on Tuesday said his country "will know what to do" if the missiles are delivered.

But on Thursday, another minister indicated Israel would only act to prevent the missiles being used against it.

"The problem arises when these arms fall into other hands and could be used against us. In that case, we would have to act," Energy and Water Minister Silvan Shalom said.

The Jewish state has already launched several air raids inside Syria this year, reportedly targeting convoys transporting weapons to its arch-foe Hezbollah in Lebanon.

Prime Minister Benjamin Netanyahu said at the end of an annual civil defence drill on Thursday that Israel was surrounded by "tens of thousands of missiles and rockets that could hit our home front".

Russia has defended its arms shipments to Syria, with Deputy Foreign Minister Sergei Ryabkov saying the missiles were a "stabilising factor" which could deter foreign intervention.

S-300s are capable of shooting down warplanes and guided missiles, and are similar to Patriots, which NATO has deployed on the Turkish border with war-torn Syria.

This month, the Wall Street Journal reported that Israel had warned the United States that Russia's plans to sell Syria the missiles would complicate any intervention to end a conflict estimated to have killed more than 94,000 people since March 2011.

Israel said Syria had been making payments on a 2010 deal to buy four batteries -- including six launchers and 144 missiles -- from Russia for $900 million (692 million euros), according to the Journal.

On the ground, fighting has centred around Qusayr, the town Assad's forces have been trying to seize back from rebels in an all-out offensive since May 19, backed by Hezbollah fighters.

The opposition warned the fierce battle for the town, strategic to both sides for its links to Lebanon and the Mediterranean, has left 1,000 wounded civilians stranded.

Syrian state television said the Arjun district in northern Qusayr, one of the few remaining rebel strongpoints, had been taken, leaving fighters there little chance to escape without being killed or captured.

"Qusayr has been under constant bombardment," said a Coalition statement, and a "large number of civilians living in the area have been injured due to the assault launched over two weeks ago on the city."

It cited an "acute shortage of doctors, paramedics and first aid kits", and said this "must trigger international relief organisations to respond immediately and save the wounded civilians".

The National Coalition has been recognised by many Western and Arab governments as the sole legitimate representative of the Syrian people.

It insists any negotiations with the regime must lead to Assad's resignation, a position Russia's Foreign Minister Sergei Lavrov criticised on Thursday as unrealistic.

"We are under the impression that the National Coalition and its regional sponsors are doing everything so as not to allow the start of the political process and achieve military intervention in Syria through any means possible," said Lavrov.

"These demands are impossible to fulfil," he said. "The only thing that unites them is a demand of Bashar al-Assad's immediate departure."