Gaza City, Gaza ? Israeli helicopters fired missiles at a group of armed men sitting near the Gaza City beach Sunday, killing four Hamas fighters, including a fugitive commander, just hours after Israel’s army chief said Hamas militants were targets for “liquidation.”

The attack occurred just 200 yards from the office of Palestinian security chief Mohammed Dahlan.

“Israel has no choice but act in those areas where the Palestinians are failing to do so,” said Gideon Meir, a senior Israeli Foreign Ministry official.

Israel’s army chief said only hours earlier that all members of the Islamic militant group were “potential targets for liquidation.” Sunday’s attack came three days after Israel killed Hamas leader Ismail Abu Shanab in a similar strike in retaliation for a Hamas bombing that killed 21 people, including five Americans, on a Jerusalem bus.

Palestinian officials said Sunday’s attack would undermine a planned Palestinian security clampdown that began Saturday with moves against arms smugglers, casting fresh doubt on an already shaky U.S.-backed peace plan. That “road map” envisions a Palestinian state by 2005.

“This aims to sabotage the efforts that began last night,” said Saeb Erakat, a senior Palestinian lawmaker. “It’s very obvious that the Israeli government is acting as if the Palestinian Authority is something from the past.”

Hamas identified the dead men as fighters Ahmed Aishtawi, Wahid Hamas, Ahmad Aub Helal and Mohammed Abu Lubda.

An Israeli military official said on condition of anonymity that Aishtawi, 24, was the main target, describing him as a senior operative who planned and committed attacks in Gaza and the West Bank.

A Hamas spokesman said Aishtawi led a unit that pioneered the firing of homemade missiles and specialized in hitting tanks.