The fragile six-month truce between Israel and Hamas in the Gaza Strip appeared set to expire on Friday, a day after spokesmen for the Palestinian militant group declared the agreement would not be extended.

The statement from two Hamas officials, who blamed Israel for the breakdown of the truce, prompted senior Israeli officials to warn that Israel will hold Hamas responsible for any escalation of violence in Gaza.

"The calm is over," Hamas member Ayman Taha said. "The calm, which was reached with Egyptian sponsorship on June 19 and expires on Dec. 19, is finished because the enemy did not abide by its obligations."

Meanwhile, another Hamas spokesman in Gaza, Fawzi Barhoum, said there was "no chance" of extending the ceasefire.

A spokesman for the Israeli foreign ministry maintained the truce had no expiration date and Israel would like to see it extended.

"We think the lull is in the best interest of both sides," Yigal Palmor said.

The truce started coming apart in early November, when Israeli troops entered Gaza and killed six militants in an incursion aimed at destroying a border tunnel the Israeli military said was under construction. Gaza rocket squads responded by resuming daily barrages into Israel's south.

On Thursday, Gaza militants fired 11 rockets and six mortar shells toward Israel, while Israel's military launched at least two air strikes on rocket squads. The week has seen at least 50 rocket attacks on southern Israel.

Despite the truce greatly reducing the level of violence in the coastal territory and bringing a dramatic drop to the number of militant rocket attacks on southern Israeli towns, both sides charged the other with violating the terms of the agreement.

Hamas complained that Israel never fully opened its border crossings with Gaza to permit the flow of international aid and fuel into the impoverished territory, which sparked shortages of goods and widespread blackouts.

Israel said Hamas, which has controlled Gaza for 18 months, used the truce to replenish its arsenal with arms smuggled in through dozens of tunnels under the territory's sealed border with Egypt.

With files from the Associated Press