Palestinian militants fired a Qassam rocket into the western Negev on Thursday as Ashkelon residents protested against an upsurge in cross-border attacks from Gaza.

The Qassam attack was the latest violation of a five-month Israel-Hamas truce in the Gaza Strip.

The rocket, which struck an open area in the Sha'ar Hanegev regional council, caused neither casualties nor property damage.

Dozens of Ashkelon residents held the protest at the entrance to the southern city.

"I call on every parent in the state, on every mother and every father, to cooperate with us, to join our protest, and to demand that the government promise [us] quiet and security," said one of the demonstrators, speaking to Israel Radio.

Gunmen from Gaza have fired dozens of rockets at Israel in the past two weeks after Israel launched a raid it said was aimed at thwarting the planned kidnapping of a soldier by Gaza militants.

Since then, Israel Defense Forces have killed about a dozen gunmen, and closed crossing points with Gaza, choking off some food supplies to the coastal territory.

UN chief to Israel: Ease Gaza blockade

Foreign Minister Tzipi Livni rebuffed a new attempt by United Nations chief Ban Ki-moon on Thursday to ease a bruising blockade of the Gaza Strip, pledging retaliation and calling on the world to condemn Palestinian rocket attacks instead, an aide to the minister said.

The humanitarian situation in Gaza has grown worse since a 5-month truce began coming apart two weeks ago. Responding to near-daily rocket attacks, Israel shut its cargo crossings with the territory. Ban - who called Prime Minister Ehud Olmert earlier this week to lobby for more aid shipments - turned up the heat on Thursday with a similar call to Livni.

In a tense conversation with Ban, Livni declared that the blockade would not end until Palestinian militants stop firing rockets at Israel, an aide to Livni reported.

"There is no way that Palestinian terrorists will shoot at us and we will not respond," Livni told Ban, the aide said. The international community must speak up and use its influence against the Palestinian rocket attacks.

The aide spoke on condition of anonymity because the telephone call was private. There was no immediate word from the UN on Ban's appeal. Israel hopes by closing cargo crossings it can force Gaza's Islamic Hamas rulers to halt militant rocket and mortar fire at Israeli border towns. But the closures have drastically reduced the flow of goods into Gaza, home to 1.4 million people.

Although some food is smuggled in through tunnels from Egypt, many basic goods are in short supply. The top UN aid official in Gaza told The Associated Press on Thursday that Israel had reversed a decision to let in 70 trucks of humanitarian aid, bringing UN aid stocks perilously close to depletion.

Israel denied it had agreed to let the aid through. "We have pinpoint intelligence warnings that they are planning a terror attack on the crossings," said Defense Ministry spokesman Shlomo Dror. "The trucks were never supposed to go through because of the rocket attacks and because of the planned attack on the crossings."

Without more supplies, the UN will be forced to suspend food distribution to 750,000 Gazans at the end of the week, said John Ging, head of Gaza operations for the United Nations Relief and Works Agency.

"We have a situation where 80 percent of the population live in abject poverty and the results of that are the daily needs are not being met by any family," Ging said.

Earlier Thursday, an explosion in the Gaza Strip killed a member of the Hamas Islamist group, hospital staff and witnesses said.

It was not immediately clear whether the man was killed by an Israel Defense Forces strike or an accidental explosion. The IDF had no immediate comment.

Also on Thursday, the Israel Defense Forces arrested 31 suspected militants south of the West Bank city of Bethlehem.