At least twelve people were killed Saturday in airstrikes that hit a rehabilitation center for the disabled in Gaza, a mosque and other targets in the area, according to Palestinian medics. It comes as the death toll from Israel's bombardment of the Palestinian enclave rose to 135.

Three patients and a nurse were killed overnight in the explosion on the rehabilitation center in Jebaliya, as Israel's campaign entered its fifth day. Video footage of the aftermath of the attack showed victims being taken to hospital for injuries, including severe burns.

Fatalities from the offensive in Gaza now include 88 civilians, 30 of which are children, according to the United Nations. More than 1,000 people have been injured in air strikes in five days of shelling, according to the Gaza Ministry of Health.

Meanwhile, Israel said 680 rockets had been fired from Gaza into Israel since Tuesday, injuring nine Israelis. On Saturday, a missile seriously wounded one Israeli and injured another seven when it hit a fuel tanker at a service station in Ashdod, 20 miles north of Gaza.

The rocket salvoes from the enclave, some striking more than 60 miles from Gaza, have so far resulted in no fatalities, due in part to interceptions by Israel's partly-U.S. funded Iron Dome aerial defense system. The Israeli army said that it had struck a total of 1,160 targets since the latest round of hostilities began earlier this week.

Alongside the dead from the rehabilitation center in Jabaliya, there were also reports of casualties at a separate charitable association for the disabled in Beit Lahiya, resulting from the latest raid.

At least two people killed and four critically wounded in the Beit Lahiya explosion, according to the AFP news agency. Meanwhile three people were killed in the eastern Tufah area of Gaza City, and three in western Gaza City, it was reported.

An Israeli military spokeswoman said she was checking for details on why the Beit Lahiya center was targeted.

A mosque in Al-Nuseirat, in central Gaza, was also destroyed in the overnight raids. Graffiti scrawled on one of the mosque's blasted walls read, "We will prevail despite your arrogance, Netanyahu."

The Israeli military said the mosque housed a weapons cache.

The United Nations Security Council, meanwhile, called for a cease-fire Saturday in the hostilities centered on Gaza. A council statement approved by all 15 members calls for de-escalation of the violence, restoration of calm and a resumption of direct negotiations between Israel and the Palestinians aimed at achieving a comprehensive peace agreement based on a two-state solution.

The press statement, which is not legally binding but reflects international opinion, expresses "serious concern regarding the crisis related to Gaza and the protection and welfare of civilians on both sides." It calls for respect for international humanitarian law, including the protection of civilians.

The U.N. and a handful of consulates are preparing for an exodus of 800 dual- and foreign-nationals from 21 countries on Sunday morning through the Erez Crossing at the northern end of the Gaza strip, according to a U.N. official.

On Saturday, Israel's army chief, Lieutenant-General Benny Gantz, said his forces were ready to act as needed — hinting at readiness to send tanks and ground troops across the barbed-wire boundary into Gaza, as Israel last did for two weeks in early 2009. Some 20,000 reservists have already been mobilized for a possible thrust into Gaza, the army said.

"We are in the midst of an assault and we are prepared to expand it as much as is required, to wherever is required, with whatever force will be required and for as long as will be required," Gantz told reporters.

The Israeli Prime Minister Benjamin Netanyahu said late on Friday that he would continue the military campaign until he achieved his goal.

"No international pressure will prevent us acting with all our force against a terror organization that is calling for our destruction,” he said. “We will continue to forcefully attack anyone who is trying to hurt us,” he told reporters in Tel Aviv on Friday, a day after a phone call with U.S. President Barack Obama about the worst flare-up in Israeli-Palestinian violence in almost two years.

"No terrorist target in Gaza is immune," he added.

Washington affirmed Israel's right to defend itself in a statement from the Pentagon on Friday. But Defense Secretary Chuck Hagel told Israeli Defense Minister Moshe Ya'alon he was concerned "about the risk of further escalation and emphasized the need for all sides to do everything they can to protect civilian lives and restore calm," a Pentagon statement said.

Al Jazeera and wire services