Gaza's central security headquarters and prison, known as the Seraya, after it was hit in an Israeli missile strike in Gaza City on Sunday. (Adel Hana/Associated Press)Two days of Israeli air strikes have claimed nearly 300 lives in Gaza amid signs that Israel is massing forces for a ground assault to stop rocket attacks by Hamas militants.

The CBC's Peter Armstrong, reporting from Israel, said Israeli jets kept up their attacks on Sunday as tanks rolled toward the Gaza border on flatbed trucks.

"The air strikes have been pounding targets inside the Gaza Strip," he said. "We saw today a major security installation, a police headquarters bombed, a mosque was hit by air strikes, a television station, they were all hit through the day."

The Associated Press estimated that more than 290 people — most of them Hamas police officers, but also 20 children — were killed in some 300 Israeli air attacks over two days.

Despite the attacks, more than 100 rockets and mortars rounds have been fired out of Gaza and into southern Israel since the Israeli operation began, Armstrong said.

Meanwhile, Israel is calling up 6,500 reserve soldiers and moving heavy equipment toward Gaza, he said.

"We passed dozens of trucks on the road bringing more armoured vehicles, armoured personnel carriers, armoured ambulances and, of course, tanks down to the area," he said. "But military experts in Israel have said that it would take at least 10,000 soldiers for a full-scale invasion."

Both Israel and Hamas drew international criticism for their attacks, with Arab countries generally condemning Israel and the United States holding Hamas responsible for a broken ceasefire and renewed violence.

Canada's foreign affairs minister, Lawrence Cannon, declared Saturday that Israel has a "clear right to defend itself" against continuing attacks by militants he accused of deliberately targeting civilians.

In Gaza, witnesses said Israeli warplanes dropped three bombs on the Seraya compound in downtown Gaza, including a prison building there.

Health officials said four people were killed and 25 were wounded in that attack.

A column of black smoke towered from the building and some prison inmates fled after the missiles struck.

Israel launched some 250 air strikes over the first 24 hours of the campaign in an attempt to quash rocket barrages from Gaza. About 600 people were wounded.

As the campaign continued for a second day, Israeli planes struck dozens of smuggling tunnels under the Gaza-Egypt border, cutting off a lifeline that had supplied Hamas with weapons and Gaza with commercial goods.

Israeli Foreign Minister Tzipi Livni told NBC that the assault was ordered because Hamas is smuggling weapons and building a "small army."

Streets were empty in Gaza City on Sunday as most residents stayed home, fearing more air strikes. A few lined up to buy bread outside two bakeries.

Schools were shut for a three-day mourning period. Hamas police kept a low profile, wearing jackets over their dark-blue uniforms and walking close to walls, hoping to evade detection by Israeli pilots.

Many Palestinians hoping to flee the chaos have been trying to cross into Egypt. On Sunday, Egyptian forces, some firing in the air, tried to push them back into Gaza and an official said one border guard was killed.

With files from the Associated Press