Updated

Two suicide bombers set off nearly simultaneous explosions Saturday in a crowded street in downtown Jerusalem, according to police.

Israeli Foreign Minister Shimon Peres said the attack was "one of the worst we have ever seen."

At least 10 people were killed by the blasts at the Ben Yehuda pedestrian mall, not including the bombers, according to reports. About 170 were injured, seven of them in very serious condition. The explosives used by the bombers were studded with nails.

"There were lots of limbs and dead bodies," said Michael Perry, 37, who ran out of a bar along the mall after hearing the blasts just before midnight local time.

"A lot of people were crying, falling, and there was the smell of burning hair," 19-year-old Eli Shetreet said.

A third blast from a car bomb parked near the mall followed shortly thereafter. It was not immediately clear whether any casualties occurred.

No group has yet claimed responsibility, but the terrorist groups Hamas and Islamic Jihad have threatened to retaliate for Israel's killing of Mahmoud Abu Hanoud, the leader of the Hamas military wing in the West Bank, earlier this month in an Israeli missile attack.

President Bush issued a statement from Camp David extending his condolences to the people of Israel and condemning the attacks "as acts of murder that no person of conscience can tolerate and no cause can ever justify."

Bush also warned that Arafat "must immediately find and arrest those responsible for these hideous murders. They must also act swiftly and decisively against the organizations that support them."

Israeli Prime Minister Ariel Sharon asked Bush to move up their meeting, formerly scheduled for Monday, in order to discuss "the most successful Palestinian terrorist attack ever on the Israeli capital." The meeting will now occur on Sunday.

In a statement, the Palestinian Authority condemned the attacks and accused those behind it of trying to derail a U.S. peace initiative.

The U.S. envoy in the region, retired Marine Corps Gen. Anthony Zinni Anthony Zinni, said in a statement that he had spoken to Palestinian leader Yasser Arafat and "made absolutely clear that those responsible for planning and carrying out these attacks must be found and brought to justice."

Israel blamed Arafat for the attacks, saying he had done little to stop in terrorism. Israeli Cabinet minister Dan Meridor said Israel was "tired of words . . . (Arafat) needs to take action immediately now because this cannot continue."

Zinni echoed the Israeli statement, saying, "this is an urgent task and there can be no delay nor excuses for not acting decisively."

"This is a great catastrophe. There are many, many casualties," said Health Minister Nissim Dahan. "We are almost at the limit of our capacity to take in the wounded."

The attacks came two days after the suicide bombing of an Israeli bus by an Islamic Jihad militant. That blast killed three passengers in addition to the bomber, 32-year-old Samer Abu Suleiman from a village near the West Bank town of Jenin.

Hours before Saturday's attacks, the Israeli army retaliated for Thursday's bus attack by moving on Palestinian-controlled towns in the West Bank, parking tanks in front of village entrances and between houses. Those movements were ordered by Israeli Prime Minister Ariel Sharon, who is currently visiting the United States, an Israeli military source said on condition of anonymity.

Four tanks sat in the middle of Haifa Street at the entrance to Jenin in the West Bank while seven tanks entered the nearby Palestinian-controlled town of Burkin, some parked in between houses, said Col. Turki Abu Ali, a Palestinian security force leader in Jenin.

The Palestinian village of al-Jabriat, near Jenin was also blocked by tanks, he said from the scene.

The Israeli army denied it was in Palestinian-controlled territory. "We're not entering the towns, we're enforcing the closure," the army spokesman said. 

Israel's actions took place just as Zinni said he would stay in the region "as long as it takes" to secure a truce.

After meeting with Israeli President Moshe Katsav in Jerusalem on Friday, Zinni said he would stick with his mission of reviving a truce deal and restarting peace talks. "I want to say that I, in the most strongest sense, condemn this violence," Zinni said, referring to Thursday's bus bombing.

"The groups that do this are clearly trying to make my mission fail . . . I am determined not to let that happen."

Jennifer Griffin and the Associated Press contributed to this report.