Israelis on Saturday marked the start of the Jewish Passover holiday with a ritual meal, or Seder, including several dozen who set up their table outside Prime Minister Ehud Olmert's residence to press him to do more to bring home three missing Israeli soldiers.

Israeli security forces were on alert, amid concerns that Palestinian militants will carry out attacks during the weeklong holiday. The Israeli military sealed the West Bank and Gaza until the end of Passover.

Earlier Saturday, Hamas suicide bombers blew up two military-style jeeps packed with hundreds of kilograms of explosives at an Israeli crossing in Gaza, wounding 13 soldiers. Hamas threatened more attacks to break the blockade of Gaza, imposed by Israel and Egypt after the Hamas takeover of the area last year.

"Hamas tried to harm the joy of the holiday," said Maj. Gen. Yoav Gallant, the Israeli military commander on the Gaza-Israel border. He said he will spend the Seder with soldiers.

Passover marks the exodus of the ancient Israelites from slavery in Egypt. The story of that flight is told during the Seder. Throughout the week, observant Jews replace bread with unleavened crackers, or matza, in remembrance of the hasty departure from Egypt.

This year, the Seder fell on the end of the Jewish Sabbath, complicating preparations. Work is forbidden during the Sabbath, meaning most arrangements had to be completed a day before.

One Seder was held outside Olmert's official residence. About 50 friends of three Israeli soldiers missing in Gaza and Lebanon set up a long table for their communal meal, part of a protest against the government's failure to bring the soldiers home.

Two of the soldiers, Eldad Regev and Ehud Goldwasser, were captured by Lebanese Hezbollah guerrillas in 2006. They were badly wounded in the cross-border raid, which sparked Israel's war against Hezbollah. The third, Cpl. Gilad Shalit, was captured by Hamas-allied militants in 2006 and is being held in Gaza.

Miki Leibowicz, 32, one of the Seder guests, said Olmert must do more to bring the three home.

"Passover is a symbol of freedom, and our friends suffer froma lack of freedom," said Leibowicz.

Before the start of Passover, the government's counterterrorism adviser urged Israelis not to travel to Egypt's Sinai Peninsula, long a popular vacation spot. Israel is worried about a growing presence of Al Qaeda-linked cells in the Sinai, where Israelis were targeted in several bombings in recent years.

In Israel, holiday shopping was brisk. Passover is also a time of family trips and gifts, and the Israeli Manufacturers Association said Israelis spent around 1.5 billion shekels, or about $441 million, on Passover foods.