In the latest air strikes, a helicopter fired a missile into a building in Gaza City that the army said was used by militants. No one was hurt. Two missiles also hit areas in northern Gaza, slightly wounding one person.

But ground forces have largely avoided clashes while Egypt mediates in a crisis that has pushed Israeli-Palestinian ties to new lows and piled pressure on the Hamas-led government, already on the brink of financial collapse from a Western aid embargo.

In their new communique, the militant groups accused Israel of bad faith in the Egyptian-led mediation effort.

There was no immediate Israeli response to the communique.

In tough comments on Monday, Olmert warned leaders of the Hamas-led government that any of them could be attacked if harm came to the abducted soldier.

Hamas' armed wing and other militants have responded by threatening to strike inside Israel.

Some Palestinian officials said Egyptian mediation was continuing but foundering because of Israel's military moves in Gaza, home to 1.4 million people.

One official with knowledge of the talks said mediators would suspend their involvement on Monday night if Hamas did not show more flexibility. Another said no deadline had been issued.

A Palestinian official has quoted mediators as saying Shalit was alive after being treated for wounds.