JERUSALEM - Israel has declared a heightened security alert over a Jewish holiday which starts Thursday and barred Palestinians from the West Bank and Gaza Strip from entering the country, fearing Hezbollah guerrillas may try to carry out a major attack.

The Purim holiday starting at sundown coincides with the end of a 40-day mourning period for Hezbollah commander Imad Mughniyeh, who was killed in a car bombing in Syria last month. Israel has denied involvement, but the Lebanese guerrilla group has blamed Israel and vowed revenge.

The alert came amid new signs that Israel is moving closer to a cease-fire with Hamas militants in the Gaza Strip. Israeli defense officials said Amos Gilad, a senior Defense Ministry official, traveled to Cairo on Tuesday for talks with Egyptian mediators. The officials spoke on condition of anonymity due to the sensitive nature of the talks.

The Israeli army said the closure would remain in effect through Sunday night, preventing thousands of Palestinian workers and merchants from entering Israel. Most come from the West Bank, but small numbers of merchants from the Hamas-controlled Gaza Strip are allowed into Israel. Palestinians needing treatment at Israeli hospitals will be able to enter, and cargo crossings will keep operating, a military spokesman said on condition of anonymity, citing policy.

While Israel typically imposes closures during major holidays, when schools are closed and public areas are crowded with travelers, security officials are even more fearful following the Mughniyeh killing. Police spokesman Micky Rosenfeld said police have canceled vacations for officers and brought in extra forces to guard festivities.

Rescue services were on high alert and extra ambulances were on standby.

The Islamic mourning period for Mughniyeh is set to end this weekend. Hezbollah is believed to have close ties with Palestinian militants in the West Bank, who in the past have carried out attacks during Purim, a holiday when young children dress up in costumes.

Violence in the Gaza Strip and southern Israel has slowed in recent weeks as Egypt pressed Hamas to stop its rocket fire and Israel to halt military strikes. The truce efforts intensified after a fierce round of fighting that began in late February and killed more than 120 Palestinians, including dozens of civilians, as well as three Israelis.

Israel has been battling Hamas since the Islamic militant group violently seized control of Gaza last June. In addition to its military activity, Israel has imposed a tough economic blockade on the area.

As part of the truce talks, Hamas wants Israel to reopen Gaza's border crossings. Hamas also wants to have some sort of presence at the crossings, and Israeli defense officials have not ruled that out, as long as Israel is allowed to monitor the passages in some way as well.

Hamas spokesman Ayman Taha confirmed Wednesday the talks were under way with Egyptian mediators.

"As we have always said, the ball is in Israel's court," Taha said. "We cannot forget that.... Every single minute they are committing new aggressions against the Palestinians."

In Washington, meanwhile, the State Department again ruled out U.S. talks with Hamas, which it designates as a terrorist organization.

"It'll be a cold day in hell before you see a change in U.S. policy with respect to discussing, winking at, nudging, looking at or otherwise dealing with a terrorist organization," deputy spokesman Tom Casey said.

He said the U.S. had no say on Egypt or other countries talking to Hamas. "Those are choices that they are going to have to make," Casey said.

Last week, Secretary of State Condoleezza Rice said she had talked with the Egyptians and "we fully expect the Egyptians to carry out the efforts that they said they would carry out to try to bring calm to the region, to try to improve the situation in Gaza."

Israeli troops at the Israel-Gaza border Thursday shot dead a Palestinian near the dividing fence. Palestinian medics said. They said the dead man was a 60-year-old farmer. The Israeli military had no immediate comment.