Israel's deadly air offensive in the Gaza Strip has sparked clashes between Palestinian gunmen and Egyptian security forces.  Nearly 300 Palestinians, most of them armed militants, have been killed since Israel launched the offensive on Saturday. 

Hundreds of Palestinians breached the Gaza border fence in four places and poured into Egypt on Sunday.  Egyptian police opened fire, prompting gun battles with Palestinian militants.  Several hours later, Egyptian officials said border guards restored order.

The breach followed Israel's bombing of 40 tunnels in Gaza used by the ruling Islamic militant group Hamas to smuggle weapons and supplies across Egypt's Sinai Peninsula.

Israeli spokesman Mark Regev says that stopping the flow of weapons to Hamas is a strategic objective. "Unfortunately, we're seeing smuggling across the border from Sinai into Gaza of both explosives and weaponry and know-how.  And that's a threat to our country," he said.

The unrest along the border worries the pro-western Egyptian government, says Israeli analyst Jonathan Spyer. "Egypt is immensely concerned about what's going on in Gaza because, of course, Hamas is the Palestinian branch of the Muslim Brotherhood and the Muslim Brotherhood is the main domestic opposition to the regime in Egypt," he said.

The breach was reminiscent of events in January, when hundreds-of-thousands of Palestinians broke through the Gaza border fence and poured into Egypt.  They stocked up on food and supplies in defiance of a crippling Israeli blockade.  Egypt has fortified the border since then because it sees a flood of Palestinians into its territory as a threat to national security.