BRUSSELS, Belgium — European governments condemned Israel's killing Monday of Hamas leader Sheik Ahmed Yassin, with several branding the airstrike a violation of international law and a blow to the stalled peace process.

The foreign ministers of the EU nations appealed to Israel and Palestinians to "refrain from acts of violence which will only lead to more deaths and will put a peaceful settlement (of their conflict) still further from reach."

Yassin, the founder of Hamas, and seven others died in a sunrise helicopter missile strike outside a Gaza City mosque. He was the most prominent Palestinian leader killed by Israel in more than three years of fighting.

Israeli officials said Yassin was responsible for scores of suicide attacks Hamas has unleashed since 2000. Palestinian militants vowed revenge attacks against Israel and the United States.

In a statement, the EU foreign ministers said Hamas was guilty of "atrocities ... which have resulted in the deaths of hundreds of Israelis" and that Israel has the right to protect itself against terrorist attacks.

"Israel is not, however, entitled to carry out extra-judicial killings," the EU statement added. It said Yassin's assassination "has inflamed the situation ... Violence is no substitute for the political negotiations which are necessary for a just and lasting settlement."

British Foreign Secretary Jack Straw said Yassin's assassination would not make Israel any more secure.

Straw spoke of "Israel's paramount need to defend itself" against terrorists, but if it wants "the full support of the international community, it needs to do so within the boundaries set by international law."

Baroness Symons, a minister in the British Foreign Office, called in Israel's ambassador to Britain, Zvi Shtauber, to express the government's concern over the killing.

She told Shtauber that while Britain believed Israel had a right to defend itself, its actions should stay within international law, the Foreign Office said.

Spain's prime minister-elect, Jose Luis Rodriguez Zapatero, said Israel's killing of Yassin proved wrong U.S. assertions that the invasion of Iraq and ouster of Saddam Hussein would bolster the cause for Middle East peace.

"There is not more security. There is too much insecurity," Zapatero said as he ended a post-election vacation in the Canary Islands.

EU foreign policy chief Javier Solana called it "very, very bad news for the peace process."

German Foreign Minister Joschka Fischer said he was "deeply concerned about the possible consequences," such as an escalation of violence.