U.S. Secretary of State Condoleezza Rice on Friday expressed American concern over Hamas' announcement that its Egyptian-brokered truce with Israel in the Gaza Strip was formally over, warning that renewed fighting would not benefit the Palestinians.

"I sincerely hope that there will not be a resumption of the violence because that is not going to help the people of Gaza," she said from Washington. "It is not going to help the Palestinians, it is not going to help the Palestinian cause."

Rice's comments came after Gaza militants fired four Qassam rockets into southern Israel on Friday, continuing the barrage of the past several days. The rockets struck the western Negev, causing neither casualties nor damage.

Minister of National Infrastructures and former defense minister Benjamin Ben-Eliezer warned earlier Friday that the Israel Defense Forces would use all its power to end the cross-border rocket attacks.

"From our point of view when the truce ended - it ended, and the IDF will operate with all its power in order to eradicate the [rocket] fire. There is a limit to what Israel is able to accept," said Ben-Eliezer.

The IDF said troops guarding Israeli farmers in fields adjacent to Gaza came under sniper fire from across the border. There were no injuries reported in any of the incidents.

In a statement posted on its Web site Friday, Hamas said Israel had breached agreements by imposing a painful blockade on Gaza, staging military strikes into the densely populated coastal strip and continuing to hunt down Hamas operatives in the West Bank.

"Since the enemy did not abide with the conditions... we hold the enemy the fully responsible for ending the truce and we confirm that the Palestinian resistance factions headed by Hamas will act," the statement said.

In light of the Hamas announcement, senior Israeli officials warned that a military offensive in the coastal territory would be "unavoidable" if the rocket fire continues.

United Nations Secretary-General Ban Ki-moon on Friday reiterated his appeal to extend the truce, immediately halt rocket attacks against Israel and all acts of violence, UN deputy spokeswoman Marie Okabe said from the world body's New York headquarters.

"A major escalation of violence would have grave consequences for the protection of civilians in Israel and Gaza, the welfare of the Gazan civilian population, and the sustainability of political efforts," Okabe said.

On Thursday, Gaza militants fired 11 rockets and six mortar shells toward Israel and Israel staged at least two air strikes against rocket squads.

The government in Jerusalem ordered the IDF to refrain from offensive operations for now, saying it wants to see how the situation develops.

"We will not be the ones to violate the cease-fire," a senior defense official said Thursday night. "If Hamas wants to escalate, we will know how to act - and it will be clear to the international community who is behind the renewed fighting."

But, a senior government official warned, "if Hamas doesn't come to its senses and calm the situation, there will be no choice other than an Israeli military response."

Egypt, meanwhile, said Friday it had received no requests that it try to patch up the Gaza truce, which went into effect six months ago.

"We have not so far been asked to exert [truce] efforts as we did in the past," said Egyptian Foreign Ministry spokesman Hossam Zaki.

Zaki defended the Egyptian policy of restricting the movement of people and and goods across the Rafah border point, Gaza's only outlet which is not under full Israeli control.

He said that to open the border fully, as demanded by many Egyptians including the main Islamist opposition group, would serve Israel's interests by giving the Israelis an excuse for washing their hands of the impoverished coastal strip.

The IDF, for its part, has raised its alert level along the Gaza border. The military canceled weekend leaves for all units stationed near the Strip and instructed units to prepare for mobilization.