At least five Israeli air strikes have destroyed much of one of Gaza's tallest apartment and office buildings, setting off huge explosions and wounding 20 people, Palestinian health officials said.

Israel had no immediate comment on Tuesday's attack.

Seventy families lived in the building, which also housed offices and a shopping complex.

Al Jazeera's Jane Ferguson, reporting from Gaza, said Israel fired three non-explosive warning missiles before the air strikes.

"The 13-storey building, contained 11 floors of residential units and two floors of commercial offices and a coffee shop. those floors also host the offices of the Ministry of Public Works and offices belonging to the political wing of Hamas movement," Ferguson said.

Since a truce between Israel and armed factions in Gaza collapsed, the death toll in the Palestinian enclave has steadily risen, with 13 more Palestinians killed in Israeli strikes since Sunday night.

On Monday, a 17-year-old boy was killed and about 25 people were wounded in a strike on a Gaza City mosque.

The Gaza religious affairs ministry said Israeli fire during the day destroyed four more mosques, raising to 71 the number of mosques destroyed over the past seven weeks.

Abdullah Mortaja, 27, a freelance journalist who previously worked for Hamas's Al-Aqsa TV, was among the latest casualties. Medical officials said he was hit by tank fire in the war-battered Shejaiya area of eastern Gaza City.

Two people wounded previously died of their injuries on Monday, raising the Gaza death toll since the July 8 start of the campaign to 2,135 with 10,915 wounded, according to the emergency services.

On the Israeli side, 68 people have been killed, the vast majority soldiers.

Trading blame

Despite the raging violence, there were signs the sides might be edging toward a new ceasefire.

Qais Abu Leila, a senior Palestinian official involved in Egyptian-mediated talks to reach a truce, said Cairo had proposed an indefinite ceasefire.

Cairo's latest initiative calls for the immediate opening of Gaza's crossings with Israel and Egypt to aid reconstruction efforts in the coastal strip, to be followed by talks on a longer-term easing of the blockade.

Hamas and Israel blamed each other for delaying an agreement.

An Israeli official speaking on condition of anonymity told the Reuters news agency that Israel would consider the proposal if Hamas were to accept it.

Hamas spokesman Sami Abu Zuhri said of Egypt's proposals that "if Israel agreed to it, we would be heading towards an agreement".

Hamas has said it will not stop fighting until the Israeli-Egyptian blockade on the enclave of 1.8 million people is lifted.

PHOTO CAPTION

Palestinians from a damaged apartment building inspect the damage to a neighboring building, the offices of the Hamas movement's Al-Aqsa satellite TV station, in Gaza City, northern Gaza Strip, destroyed by an Israeli strike, Tuesday, July 29, 2014.

Aljazeera