An amateur video showed two men

It was one of the bloodiest battles in nearly a year of fighting in the West Bank and east Jerusalem and raised the likelihood of further bloodshed. Israeli police said they were on heightened alert, while the Hamas militant group in Gaza said its patience was “running out.” Islamic Jihad, another militant group, vowed to retaliate.

Among the dead were two Palestinian men, ages 72 and 61, and a 16-year-old boy, according to health officials.

The four-hour operation left a broad swath of damage in a centuries-old marketplace in Nablus. In one emotional scene, an overwhelmed medic pronounced a man dead, only to notice the lifeless patient was his father. An amateur video showed two men, apparently unarmed, being shot as they ran in the street.

Israel has been carrying out stepped-up arrest raids of wanted militants in the West Bank since a series of deadly Palestinian attacks in Israel last spring.

Israeli officials liken these operations to “mowing the lawn,” saying they are necessary to prevent a difficult situation from turning worse. But the raids have shown few signs of slowing the violence, and in cases like Wednesday's operation, they raise the likelihood of reprisals.

The Israeli military said it entered Nablus, the West Bank’s commercial center, to arrest three militants suspected in previous shooting attacks. The main suspect was wanted in the killing of an Israeli soldier last fall.

The military usually conducts raids at night in what it says is a tactic meant to reduce the risk of civilian casualties. But military spokesman Lt. Col. Richard Hecht said forces moved quickly after intelligence services tracked down the men in a hideout.

Hecht said that Israeli forces surrounded the building and asked the men to surrender, but instead they opened fire. One militant who tried to flee the building was shot and killed. He said the military then fired missiles at the house, flattening the building and killing the other two men.