Israel upped the pressure on Hamas Tuesday, with warplanes hitting two Gaza City highrises on day 50 of their conflict as the warring parties mulled a new Egyptian truce proposal.

There appeared to be little outward sign, however, of interest in the Egyptian proposal which seeks to broker a more permanent end to seven weeks of fighting in Gaza which has so far killed 2,137 Palestinians and 68 on the Israeli side.

Several back-to-back truce agreements which brought relief to millions earlier this month, collapsed in a storm of violence on August 19, with the renewed fighting killing another 116 Palestinians and an Israeli child.

Israel, which pulled its negotiating team out of the Cairo talks a week ago, has repeatedly said it would not negotiate under fire, conditioning a return to the table on a complete halt to cross-border rocket fire.

Although the Palestinians said they would be prepared to accept the new Egyptian offer, they would only do so after hearing Israel's response to the proposal, a senior official told AFP on Monday.

On the battlefront, Israeli warplanes kept up their pressure on Hamas with air strikes killing six and raids hitting two high-rise apartment blocks in Gaza City, leaving 40 people wounded.

In the first strike, warplanes fired at least six rockets at a 16-storey complex in the Nasser neighbourhood, in which there were 60 apartments and a commercial complex, completely destroying the building and wounding 25.

But no-one was killed after the army warned residents to leave in a pre-recorded message, a witness told AFP. "The army told them to leave immediately and they all ran out into the street to find shelter," he said.

Warplanes then fired on the 14-storey Al-Basha building in Rimal neighbourhood, causing massive damage and wounding 15, witnesses and medics said.

The Israeli army acknowledged hitting buildings serving as "Hamas command and control centres" as well as two schools in central and northern Gaza from which "low-trajectory fire" had been directed at Israel.

In an Arabic-language text message sent to residents' mobile phones after the strikes, the army said the towers were hit because they were "used by Hamas for military purposes" and warned that the battle would continue.

- 'We escaped by a miracle' -

Hamas spokesman Fawzi Barhum denounced the bombardment of the two towers as "a war crime aimed at terrorising the people".

The group's armed wing confirmed firing on Tel Aviv and Haifa in response, although the army said nothing had hit further north than Ashkelon, where a rocket hit a bungalow causing major damage and wounding 21.

Yuval Cohen, owner of the house, said the family was sleeping when the air raid sirens sounded, saying it was a miracle they had not been killed.

"We were in our bedroom when the alarm started. We ran to the children's room to wake them and while we were running with the kids, the rocket exploded in the bedroom," he told AFP.

"Luckily, we escaped by a miracle. We didn't even make it to the shelter.

"We don't sleep at nights, we don't sleep during the days, we don't rest at all. Everybody says 'it won't happen to me' but in the end, it did."

Since midnight, 69 rockets have been fired at Israel, 61 of which struck the south while another six were intercepted, the army said.

"The goal of the fighting isn't to finish off every last launcher, the goal is to convince the other side to say 'enough'," a senior Israeli military official told Haaretz newspaper, saying Hamas was quite close to that point.

- Waiting for Meshaal -

Political officials also believe most of the Islamist movement is looking for a quick end to the conflict, particularly after three of its senior military commanders were killed in a targeted assassination last week.

"The targeted killings have created a situation in the last week in which Hamas wants a ceasefire," said Science Minister Yaakov Peri, an observer in the eight-member security cabinet.

"The man who is digging in his heels... is Khaled Meshaal," he said, referring to the movement's exiled leader who is based in Doha.

Haaretz's military correspondent Amos Harel said Meshaal was "the last obstacle on the way to declaring a ceasefire," noting that the assassinations had bolstered his position in relation to the movement's Gaza-based leaders.

Meanwhile, Abbas was to convene a meeting of his leadership in the West Bank city of Ramallah later Tuesday, officials said.

Although Israeli officials have refused to comment on the Egyptian truce proposal, army radio said Prime Minister Benjamin Netanyahu had been locked in discussions late into the night with the defence minister and the chief of staff.

A Palestinian official told AFP on Monday that the proposal would involve the easing of restrictions at border crossings into the battered enclave and allow for the delivery of aid and reconstruction materials.

"The disputed points will be discussed in a month," he told AFP, saying they were waiting for Israel's response.