West Bank (search) assailant detonated a large bomb near a busy Israeli military checkpoint Wednesday, killing two Palestinian men and wounding 16 people, mostly civilians, in an attack that prompted rare Palestinian complaints about militants responsible for scores of bombings over the past four years.

The Al Aqsa Martyrs' Brigades (search), a violent group that has carried out scores of attacks on Israelis, claimed responsibility for the attack, but apologized for the Palestinian casualties. The 16 wounded included 10 Palestinians and six Israeli border policemen.

Al Aqsa said the intended target was Jerusalem and the assailant hastily set off the 44 pounds of explosives by remote control near the Kalandia checkpoint (search) north of the city when he felt Israeli security forces were closing in on him.

The blast went off between two cars, sending a cloud of black smoke into the air as a large crowd of Palestinians was waiting to cross Kalandia. Thousands cross the checkpoint every day, and the bomber's apparent disregard for Palestinian civilians touched off an emotional confrontation in a West Bank emergency room where some of the wounded were being treated.

Zakiyah Abu Sneineh, whose 60-year-old husband, Salah, died in the blast, refused to acknowledge that he was killed by Palestinians. "Arabs couldn't have killed him, only Israelis," she said, sobbing in the emergency room of a Ramallah hospital. In an adjacent room, her 6-year-old grandson Mahdi, who was critically wounded in the blast, was fighting for his life.

The Abu Sneinehs were in their car, waiting in a line of vehicles, when the blast went off.

A Palestinian man hurt in the attack said it was too early to judge the militants. "I don't want to blame them," said Rateb Abu Fkhaideh, 47, who had a leg injury.

His comments angered several Palestinians in the emergency room. "Why are you defending them (the militants)?" 35-year-old Nader Omar asked Abu Fkhaideh. "They are wrong. We should raise our voice against them. These guys don't use their minds." Two others nodded in agreement.

In four years of Israeli-Palestinian fighting, support for the militants in Palestinian society has remained high, despite the hardships from Israeli retaliation for scores of bombings and shootings. From time to time, criticism of the militants is voiced. However, while Palestinians may complain in private, they rarely express their misgivings openly.

Elsewhere, a senior U.N. official told the U.N. Security Council on Wednesday that both Israel and the Palestinians are violating their international legal obligations and undermining prospects for peace.

Undersecretary-General for Political Affairs Kieran Prendergast (search) said Israel has an obligation to protect Palestinian life and not to destroy property unless there's an absolute military need. He said the Palestinian Authority has obligations "to protect Israeli civilians from attacks emanating from territories in its control."

Since the outbreak of fighting, 3,049 people have been killed on the Palestinian side and 970 on the Israeli side. Several Palestinians have been killed and scores wounded in attacks by militants, often while spending time in Israeli malls, cafes or outdoor market, or while riding on buses.

Palestinian officials were reserved in their criticism of Al Aqsa, which has ties to Yasser Arafat's ruling Fatah movement. "Such attacks harm the Palestinian cause," Hassan Abu Libdeh, the Palestinian Cabinet secretary, said of Wednesday's bombing. "These groups must avoid every spot where there is a possibility that a Palestinian will be there."

In Washington, State Department spokesman Adam Ereli said the United States condemned the bombing. "In our view, this once again underscores the need for the Palestinian leadership to take immediate and credible steps to end terror and violence," he said.

Zakariye Zubeydi, 29, a leader of Al Aqsa in the West Bank town of Jenin, told The Associated Press the assailant had been instructed to attack Israelis in Jerusalem. A tightening Israeli security cordon forced him to detonate the explosives near Kalandia, Zubeydi said, adding that the bomber got away.

Zubeydi apologized for Palestinian casualties. "We didn't expect people to be killed," he said.

Later Wednesday, Israeli troops sealed off Jenin and two tanks deployed on the outskirts of the town — possible preparations for a military raid.

Wednesday's bombing was the first since July 11, when Palestinian militants set off explosives near a bus stop in Tel Aviv, killing a soldier and seriously wounding at least five people. In recent months, the pace of Palestinian bombing attacks has slowed considerably, compared to the first three years of the current round of fighting, which began in September 2000.

Israeli security officials have attributed the change to a greater success in fighting the militants, including mass arrests, better intelligence information and a contentious separation barrier Israel is building along the West Bank.

Also Wednesday, Israeli troops shot and killed a 17-year-old Palestinian in the Balata refugee camp near the West Bank city of Nablus, local residents said. The army soldiers fired at a Palestinian who hurled a firebomb at them.

Israeli forces fired missiles Wednesday in open spaces in the Rafah refugee camp, Palestinians said. No one was hurt.