As Arabs poured into the streets Monday demanding revenge, the leaders of Egypt and Jordan, who put their prestige on the line in Mideast peace efforts, denounced Israel's assassination of the founder of Hamas (search).

Arabs demonstrated by the thousands in refugee camps and on university campuses in Egypt, Lebanon, Syria, Jordan, Iraq, the Palestinian territories and Yemen in loud but generally peaceful protests, burning tires or Israeli flags and demanding revenge for Israel's killing of Sheik Ahmed Yassin (search), spiritual leader of Hamas militants.

Anti-Israel sentiment has meant Arab peace efforts always are discussed quietly and carefully, but Jordan and Egypt have been heavily involved recently in trying to restart the long-stalled Israeli-Palestinian process.

On Monday, they acknowledged it could go nowhere right now.

"What peace process, when the situation is on fire?" a fed-up President Hosni Mubarak (search) retorted to reporters asking about the impact of Yassin's death. "Nobody would have imagined that matters would go this far. ... Its repercussions are unknown."

He said Egypt is aborting its efforts to get negotiations back on track.

King Abdullah II of Jordan — who met secretly with Israeli Prime Minister Ariel Sharon (search) as recently as Thursday to discuss a proposed Israeli pullback from parts of the West Bank and Gaza Strip — said the assassination would only lead to more violence and instability.

"We are annoyed and pained by what happened despite our arduous and persistent efforts with all sides, including the Israeli government, to refrain from its policy of military escalation," Abdullah said in remarks on Jordan's official Petra news agency.

Mubarak canceled a planned visit by some Egyptian legislators to take part in Israeli parliament ceremonies Tuesday marking the 25th anniversary of the Egypt-Israel peace accord.

Despite limited results, Egypt's peace push had left Mubarak open to criticism from opponents of Israel. Yassin's killing fuels their arguments.

"This is an embarrassment to Egypt," said Dia'a Rashwan, an expert on radical Islam with Al Ahram Center for Political and Strategic Studies in Cairo. "Egypt was directly involved in bringing Hamas and Jihad closer to the Palestinian Authority and bringing about a cease-fire. Targeting Yassin is a direct blow to these efforts."

After the killing, the foreign ministers of Jordan and Syria changed their schedules to fly to Cairo for urgent talks with their Egyptian counterpart. The matter also was to be discussed by the "Quartet" — representatives of the United States, Russia, the European Union and the United Nations — at the U.S. Embassy in Cairo.

Arab leaders have been working through the 22-nation Arab League to try to reinvigorate their 2002 call for a solution to the Palestinian crisis. More directly, Mubarak and senior Egyptian officials have been consulting with the Israelis on Sharon's pullback plan, arranging for Egypt to tighten its border security and help the Palestinian Authority prepare to take control of the volatile Gaza Strip.

In Washington, U.S. National Security Adviser Condoleezza Rice urged calm and said she hoped new opportunities, such as the Israeli pullout plans, would continue to emerge.

Rice told NBC the Bush administration received no advance warning of the strike. However, she added that "Hamas is a terrorist organization and that Sheik Yassin has himself, personally, we believe, been involved in terrorist planning."

U.N. Secretary-General Kofi Annan condemned the killing and appealed for calm. "Such actions are not only contrary to international law, but they do not do anything to help the search for a peaceful solution," Annan said.

Other condemnations and calls for restraint came from around the world. British Foreign Secretary Jack Straw echoed the sentiments of many Arab officials, saying the killing "is unacceptable, it is unjustified and it is very unlikely to achieve its objectives."

Sheik Salman al-Odah, who heads the Islam Today Organization in Saudi Arabia, said the United States, Russia, Australia and Japan should "be ashamed of their calls to the Palestinians for self-control. ... The people, governments and civil institutions of the Islamic world should intensify their financial and political support to the Islamic resistance in Palestine until it restores its rights."

Yassin's killing also ignited fresh anger against the United States, which many Arabs say could insist Israel stop its policy of "targeted killings" — strikes that Arabs consider assassinations to eliminate any Palestinian leader Israel doesn't like.

Thousands of students demonstrated in Cairo, burning American and Israeli flags.

"When Sharon crosses the line, we must kill him and his soldiers," about 7,000 students chanted at Cairo's Al-Azhar University. Similar protests were held in Lebanon, Syria, Jordan and in Yemen.

Islamists also offered their congratulations on Yassin's death — in being killed by Israeli forces, he became a martyr to his cause.

"He is not just a symbol for Palestine or Hamas, but for the entire Islamic world, and this assassination will add fuel to the resistance," said Essam el-Erian, a senior member of Egypt's Muslim Brotherhood.

In Jerusalem, the deputy director-general of Israel's Foreign Ministry, Gideon Meir, said he hoped the assassination would not hurt Israel's relations with Egypt and Jordan.

"It's in the mutual interest of all sides to continue the peace process," Meir said. "Even if peace is cold, it's still a peace."