President Bush denounced as "heavy-handed" an Israeli warplane's missile attack on a Gaza City apartment building, which killed a Hamas leader at the top of Israel's most-wanted list and at least 14 other Palestinians, including nine children.

"This heavy-handed action does not contribute to peace," White House spokesman Ari Fleischer said Tuesday, pointing to "the loss of innocent life."

"This message will be conveyed to Israeli authorities, and the United States regrets the loss of life," the spokesman said.

Fleischer rejected comparisons between the missile strike and American attacks in Afghanistan that have killed civilians.

"It is inaccurate to compare the two, because the United States, because of an errant bomb, a mistake in a mission, has occasionally engaged in military action that we very regrettably included losses of innocent lives," Fleischer said.

"This was a deliberate attack on the site, knowing that innocents would be lost in the consequences of the attack," he said, adding that Bush still remained a strong backer of Israel.

With his condemnation, the White House joined European and Arab nations who called the strike irresponsible and denounced the civilian deaths.

Palestinians vowed revenge as they dug through wreckage from the strike, which obliterated a three-story building and destroyed or badly damaged several adjacent ones.

The attack killed Salah Shehadeh, 48, a founder and the top commander of Hamas' military wing, known as Izzadine el-Qassam, the group said. The group has carried out scores of attacks, including more suicide bombings than any other Palestinian faction in the current Mideast conflict.

"This operation was in my view one of our biggest successes," Israeli Prime Minister Ariel Sharon told Cabinet ministers. "We hit perhaps the most senior Hamas figure on the operational side," Sharon said of Shehadeh, who was jailed first by Israel, and then by the Palestinians, from 1988 to 1999.

But by firing a powerful missile into a densely packed neighborhood in the middle of the night, civilian casualties were a certainty, Palestinians said.