The U.N. agency for Palestinian refugees said Friday it has halted all aid shipments into the Gaza Strip due to interference by the ruling Hamas militant group.

The U.N. Relief and Works agency said it made the decision after Hamas personnel intercepted an aid shipment for the second time this week.

In a statement, UNRWA said 10 truckloads of flour and rice that had been delivered into Gaza on Thursday were taken away by trucks affiliated with the Hamas-run Ministry of Social Affairs. Earlier this week, Hamas police took thousands of blankets and food parcels meant for needy residents.

UNRWA said the suspension would remain in effect until the aid is returned and the agency receives credible assurances from the Hamas government that such thefts will end. There was no immediate reaction from Hamas.

UNRWA spokesman Chris Gunness said the agency would continue to distribute aid from its existing supplies in Gaza, but that stocks were running low.

"There is enough aid for days, not weeks," he said. Complicating the situation, he said the agency has not been able to import plastic bags used for food distribution, and that existing supplies will run out early next week.

In Gaza, Hamas spokesman Fawzi Barhoum called UNRWA's decision "unjustified."

He said Hamas supports UNRWA's work but believes the agency gives some of its aid to groups attached to Hamas' rivals.

He urged UNRWA "to put an end to using aid for political means, and to distribute it to all the needy equally."

Some 80 percent of Gaza's 1.4 million people rely on the U.N. agency for food and other support, and U.N. officials say the need for aid has increased since Israel ended a military offensive in Gaza last month.

The offensive, meant to halt years of Hamas rocket attacks on southern Israel, killed nearly 1,300 people and caused widespread destruction.

Also Friday, Israel deported 15 activists from an aid ship it intercepted en route from Lebanon to Gaza. The activists, all Lebanese and Syrian citizens, were deported overnight, the military said.

Three others — two Indians and a Briton — remained in police custody pending deportation, police spokesman Micky Rosenfeld said.

The ship had attempted to reach Gaza on Thursday in defiance of an Israeli blockade. Israel intercepted the vessel and towed it to Ashdod port, where it remained docked Friday. It was not immediately clear when the boat would be allowed to sail.

Israel and Lebanon are officially at war. Israel said it was concerned about the ship's cargo and called the boat a "provocation." Israel, which is enforcing a naval blockade aimed at Gaza's Hamas rulers, has allowed several similar aid ships into Gaza and has turned several more back, but had never before boarded or detained one.

While the boat remained docked, some 1,000 units of donated blood were quickly unloaded and sent into Gaza, military spokesman Peter Lerner said. The rest of the supplies on board were being examined and would also be sent to Gaza, he said.

Israel imposed the blockade after Hamas seized control of Gaza in June 2007. Since then, it has allowed in little more than basic humanitarian supplies.

Despite Israeli concerns, no weapons were found on board. The organizers of the aid ship, Lebanese political and human rights activists, said the cargo comprised of medicine, food, toys and basic humanitarian supplies such as mattresses and blankets.

Israel unilaterally halted its devastating Gaza operation on Jan. 18, and Hamas followed with an announcement that it would hold its fire.

Sporadic fighting has persisted. On Friday, Gaza militants launched two more rockets into Israel, the military said. There were no injuries, but it illustrated the fragility of the Gaza cease-fire. Late Thursday Israeli forces on the Gaza-Israel border shot and killed a Palestinian who the military said approached the fence armed with a grenade.

Egypt's attempts to mediate a long-term cease-fire have not succeeded so far. Hamas is demanding that Israel open Gaza's blockaded border crossings as part of any agreement, but Israel says it will not turn the crossings over to Hamas control. It also wants international guarantees that weapons smuggling into Gaza will stop.

The attempts to negotiate a cease-fire are unfolding in the shadow of Israel's national election on Tuesday, as Israel's leaders compete over who can take the toughest stand against Hamas.

New polls Friday showed the likely winner would be hard-line Likud Party leader Benjamin Netanyahu, who says the current government ended the Gaza operation too early, without causing enough damage to the Islamic group.