A Palestinian mortar attack Monday on one of the two remaining open passageways into Gaza didn't stop Israel and the United Nations from bringing humanitarian aid into the area, according to Shlomo Dror, a spokesman for the Coordinator of Government Activities in the Territories. The attack forced Israel to close the Kerem Shalom crossing for the day, Dror told The Jerusalem Post. Israel, however, hopes to reopen it as soon as possible and plans to continue the flow of basic aid through Kerem Shalom as well as Sufta, he added. Even with Monday's closure of the Kerem Shalom crossing, Israel managed to facilitate the passage of 99 trucks with supplies into Gaza through Sufta, said Dror. Islamic Jihad took responsibility for the Kerem Shalom attack in an announcement on its Web site. Ahmed Youssef, an aide to deposed Prime Minister Ismail Haniyeh of Hamas, read a statement denouncing the attack. "The crossings should be out of the range of mortars from the factions out of concern for people's lives and livelihoods," he said. Some 1.1 million of the 1.4 million people in Gaza are dependent on basic staples of flour, rice, sugar, lentils and powdered milk that are handed out to them by the United Nations. The continued passage of those goods into Gaza, along with medicines and animal feed, had been diverted in the last week from the primary commercial passageway of Karni, that had been closed since Hamas took over Gaza 10 days ago. Instead a plan was finalized on Sunday by Israel, with the assistance of the UN, to allow basic supplies into Gaza through two secondary crossings, Kerem Shalom and Sufta. That plan was still in place, said Dror who added that Israel was committed to ensuring that humanitarian aid enters Gaza. "We have this lifeline open at the moment and everyone is doing their best to keep it open," said John Ging, who heads the United Nations Relief and Works Association effort in Gaza. He added that he hoped that the attack was an isolated incident. "This is exactly the operational challenge that is faced to keep the crossings going. We hope that this is not the beginning of sustained attacks because everyone knows how vulnerable the humanitarian situation is there," Ging told the Post. A spokesman for UNRWA in Jerusalem, Christopher Gunness, said that Israel had been very creative and helpful in getting basic supplies into Gaza. But he added that the push was to get Israel to reopen Karni so that the crippled Palestinian economy would not deteriorate even further than it has. There is a larger crisis of poverty and unemployment looming if commercial activity cannot resume, he said. Among the more immediate casualties of the Karni closure could be the United Nations Development Program, which on Monday announced that it would be forced to suspend its infrastructure projects in Gaza if building material and supplies were not let in soon. It had been working on projects involving water, sewage treatment, roads, community centers, schools and housing. But Dror said that Karni was not closed as a punishment to the Palestinians. Kerem Shalom and Sufta were in use precisely because it was impossible to open Karni for security and technical reasons, said Dror. It was easier to secure Kerem Shalom and Sufta than Karni because they were slightly set back from the border, said Dror. But even then, as was evident Monday, the Palestinians were able to attack the crossing by throwing mortar shells, said Dror. In Karni there was also the danger that Palestinians could get close enough to open fire, said Dror. Technically it is also hard to open Karni because much of the terminal on the other side was destroyed during the fighting between Fatah and Hamas. Finally, Fatah had manned the border and in their absence there was no one to talk with, Dror said. If the UN wanted Karni reopened, he suggested that their concerns were best addressed to Hamas. Until Monday, he said, he had hoped that Hamas would at least help secure the passage of humanitarian aid by preventing violent at the crossings, but the mortar attack proved otherwise. "There is an absurd situation where we are worrying about the Palestinians more than they are," said Dror. In the last week, aside from basic supplies, Israel has allowed fuels such as gas, petroleum, and diesel into Gaza. Medicines have gone in through the Erez crossing which has also been open to limited pedestrian traffic, including the transfer of Palestinians in need of medical treatment in Israel. The Rafah crossing into Egypt that had been manned by Fatah has been closed by the Hamas takeover. Dror said his more immediate concern this week was insuring that enough wheat entered Gaza. That shipment needed to be increased, said Dror. AP contributed to this report.