There has been more fighting between Israeli forces and Palestinian gunmen in and around the Gaza Strip. Robert Berger reports from the VOA bureau in Jerusalem.

Palestinian militants fired more than a dozen rockets at Israel putting further strain on a five-month-old cease-fire. Israel responded with an air strike. Several Grad rockets crashed into the major Israeli city of Ashkelon, marking a dangerous escalation. The Grads have a longer range than homemade Palestinian rockets and the Israeli military says they were smuggled into Gaza through tunnels under the border with Egypt.

Israeli spokesman Mark Regev threatened tougher military action.

"These attacks simply must stop," he said. "Everyone understands, the current situation is simply not sustainable. The current situation will simply not continue."

Fighting erupted 10 days ago after Israel launched a cross-border raid that it said prevented an attack aimed at kidnapping of Israeli soldiers.

Israel has shut its border crossings into Gaza in response to the rocket attacks, halting the shipment of food and supplies and creating the prospect of a humanitarian crisis. Chris Gunness is the spokesman for the United Nations agency that cares for Palestinian refugees.

"We have no food, our warehouses are empty," Gunness said. "People will start getting hungry. And therefore, our food distributions to some 750,000 of some of the most disadvantaged and impoverished people in this region are now suspended."

There are also some power blackouts in Gaza because of a shortage of fuel.