Palestinian President Mahmoud Abbas Saturday said Israel's blockade of the Gaza Strip was a "war crime," as the United Nations closed its food aid distribution centers in Gaza on Saturday.

"I would like to draw the attention of the international community to the tragedy that our people are enduring in Gaza and I call on them to intervene to end the unfair siege... which constitutes a war crime against our Palestinian people," Abbas said in published remarks.

The UN said it had to close the centers after the blockade, imposed in response cross-border rocket attacks, depleted its food reserves.

Israel sealed Gaza's borders nearly two weeks ago as part of a new round of fighting between the Israel Defense Forces and Gaza's Hamas rulers.

The clashes, including Hamas rocket fire on Israeli border towns and Israel Air Force strikes on Gaza militants, have eroded a truce that had largely held for five months.

The UN secretary general, Ban Ki-moon, called on Israel to open the crossings to humanitarian aid and also condemned the rocket fire on Israel.

"Measures that increase the suffering of Gaza's civilians are unacceptable and should cease immediately," he said in a statement.

In the Shati refugee camp near Gaza City, hundreds of people walked away empty-handed from a UN food distribution center Saturday. A note taped to the center's blue gate said that the day's round of distributions was put off until Dec. 13 because of a lack of food to distribute.

In all, the UN Relief and Works Agency distributes food to some 750,000 Gazans, or nearly half the territory's population. The needy get a new parcel of rice, flour, sugar and oil every three months. On Saturday, it would have been the turn of some 20,000 Gazans to pick up food supplies, UN aid officials said.

PA official: Abbas, Olmert to meet Mon. over Gaza violence

A Palestinian official said Saturday that Abbas will meet with outgoing Prime Minister Ehud Olmert in Jerusalem on Monday and raise his concern about renewed Gaza fighting.

A five-month-old truce between Gaza's Hamas rulers and Israel started unraveling last week as violence along the border was renewed. On Friday, at least 16 Qassam rockets were fired from Gaza into the western Negev. One Israeli sustained minor shrapnel wounds.

Negotiator Saeb Erekat said Saturday that President Mahmoud Abbas will also bring up continued Israeli settlement expansion in his talks with Prime Minister Ehud Olmert.

The two leaders have met regularly for the past year as part of U.S.-backed peace talks. However, all sides have acknowledged that they will not be able to achieve the end-of-year target for a peace deal.

Erekat says the two leaders will continue meeting to talk about bilateral concerns until the end of Olmert's term in three months.