The Israeli military announced the soldiers' deaths on Sunday, but did not immediately provide details on how the soldiers had died.

"Thirteen soldiers from the Golani Brigade were killed in Gaza overnight," a spokesperson told the AFP news agency.

"Since last night, 13 soldiers from the IDF's (Israel Defense Forces) Golani Brigade were killed while fighting Hamas terrorists in Gaza," the military said via the micro-blogging website Twitter.

This makes Sunday the deadliest single day for Israeli soldiers in years, and brings the total number of soldiers killed since Israel launched its ground operation in Gaza late on Thursday to 18.

Earlier, the Islamist militant group Hamas claimed to have ambushed Israeli troops and detonated explosives around their vehicle in the Gaza Strip. A separate militant group claimed to have attacked Israeli soldiers in a house in Gaza.

Gaza health officials, meanwhile, said 87 Palestinians had been killed on Sunday alone, pushing the total Palestinian death toll from Israel's 13-day-long offensive to 425. Most of Sunday's casualties came in the Shijaiyah neighborhood, located between Gaza City and the Israeli border. Palestinian officials put the number of people displaced by the air and ground campaign at around 35,000.

The Israeli army said it was hitting Shijaiyah because almost 10 percent of the 1,700 rockets fired at the Jewish state since it began an air offensive on Gaza on July 8 had come from the neighborhood.

"We are mobilizing in order to strike Hamas where it hurts," said Lieutenant-Colonel Peter Lerner, an Israeli military spokesman.

Prime Minister Benjamin Netanyahu told US news broadcaster CNN that he believed the operation to destroy tunnels used by Hamas and other militant groups could be completed "fairly quickly," but refused to provide a specific timeframe.

Kerry to travel to the region

Speaking in a number of US media, American Secretary of State John Kerry said he expected to travel to the region soon to try to broker an end to the violence. He also urged Hamas to accept a ceasefire with Israel.

Even a two-hour long truce brokered by the Red Cross to allow it to retrieve the dead and injured quickly became unraveled on Sunday after Israel claimed its troops were shot at by militants.

Hamas didn't immediately respond to the allegation.

pfd/msh (AFP, AP, dpa, Reuters)