GAZA (Reuters) -Israeli helicopter gunships struck targets inside Gaza and tanks probed its northern border on Monday after Prime Minister Ehud Olmert ordered the army to step up operations to free an abducted soldier.

Olmert also warned leaders of the Hamas-led Palestinian government that any of them could be attacked.

The crisis has pushed Israeli-Palestinian ties to new lows and piled pressure on the Palestinian government, already on the brink of financial collapse from a U.S.-led aid embargo.

Israeli tanks and armored bulldozers pushed inside northern Gaza just after dawn but a military source said the operation did not mark the start of a threatened large-scale incursion.

“This is not a massive ground entrance. This is a pin-point operation to locate tunnels and explosives near the border fence,” said the source.

A helicopter fired a missile into a building in Gaza City that the army said was used by militants.

The Fatah movement of moderate President Mahmoud Abbas said the office hit was a charity. Hamas also has an office there, witnesses said. There were no casualties.

Two missiles also hit areas in northern Gaza, near the town of Beit Lahiya. One person was lightly wounded, witnesses said.

Olmert’s threats came after Israeli aircraft carried out a missile strike on the empty office of Prime Minister Ismail Haniyeh of Hamas on Sunday.

“I have said, and will repeat, nobody will be immune,” Olmert said.

Israel, which pulled out of Gaza last year, sent troops and tanks into the south of the territory last Wednesday after Palestinian gunmen, some from Hamas’s armed wing, seized Corporal Gilad Shalit in a cross-border raid a week ago.

It has kept on hold a threatened major push into northern Gaza.

Hamas’ armed wing and other militants have responded to the offensive by threatening to strike inside Israel.

“We and the brothers of (Hamas’s armed wing) will carry out earthquake like attacks against the Zionists,” said Abu Qusai, a spokesman for Fatah’s al-Aqsa Martyrs Brigade.

Some Palestinian officials said Egyptian-led efforts to free Shalit were continuing but foundering because of Israel’s assault on 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.

“The situation is so complex now that I’m hoping against hope that it will have a peaceful end,” said Saeb Erekat, a senior aide to Abbas.

A Palestinian official has quoted mediators as saying 19-year-old Shalit was alive after being treated for wounds.

After Shalit’s abduction, Israel launched air strikes against Gaza’s main power plant and road bridges.

Israel has also detained a third of the cabinet and nearly two dozen Hamas lawmakers in the West Bank, and forced many other top officials into hiding.

Israel’s internal security chief Yuval Diskin told the cabinet that the crisis might take months to resolve.

At least five militants have been killed in the overall operation, a low death toll by the standards of the Middle East conflict.