Much of the world condemned the start of war against Iraq today, as numerous governments said the U.S.-led assault was not justified and hundreds of thousands of demonstrators protested in front of heavily fortified American embassies, shouting slogans criticizing President Bush.

China and Russia issued surprisingly strong denunciations of the conflict. Leading European opponents such as France and Germany were critical but seemed to mute their comments. They stressed their desire for a short war with humanitarian relief for civilian victims.

The United States' allies in the war, including Britain, Spain and Japan, defended the importance of disarming Saddam Hussein's government. In Italy and Australia, however, pro-war government statements were accompanied by substantial public protests. Pakistan, a key U.S. ally in the war against terrorism, avoided direct criticism of the United States while deploring the start of hostilities.

Antiwar demonstrations were reported in scores of cities across the globe. In Berlin, 50,000 protesters, mostly students, marched past the U.S. Embassy and through the Brandenburg Gate. Up to 40,000 protesters stopped traffic for a time in Melbourne, Australia.

More than 100,000 people, many of them high school and university students, marched to the U.S. Embassy in Athens, chanting "No to the war" and "Americans, killers of people," while an estimated 45,000 people turned out in Milan, and about 10,000 youths demonstrated in Paris at the Place de La Concorde, beside the heavily guarded U.S. Embassy.

Here in Brussels, a large crowd of protesters shook their fists and shouted "Bush, murderer!" as they pressed against barbed-wire barricades protecting the U.S. Embassy. Police in riot gear stood nearby.

"No to the massacre of civilians and the destruction of Iraq for petroleum," said a hand-painted banner at the Brussels protest. "No war for oil. Stop the USA," said a number of printed cardboard placards.

Some of the most pointed opposition came from Beijing and Moscow, both veto-wielding members of the U.N. Security Council. They have been against the war all along, but were less active than France in the recent diplomatic activity.

"We strongly urge relevant countries to immediately stop military action," a Chinese Foreign Ministry spokesman told reporters.

Without mentioning the United States by name, he said the attackers "ignored the opposition of most countries and peoples of the world." He said the war "constitutes a violation of the U.N. charter and the basic norms of international law."

Chinese analysts said the tough stance was aimed at China's domestic audience. They predicted the government will use the attack as another way to criticize the United States, and by association its political system.

But China is unlikely to allow its criticism to affect U.S.-China ties, the analysts said. To that end, Beijing has rejected applications by student groups to demonstrate against the war, and it has ensured that China's state-controlled media have been generally free of the anti-American screeds that were popular during the U.S.-led attacks on Yugoslavia in 1999.

President Vladimir Putin of Russia called the attack indefensible and "a big political mistake" in a short address on national television. "Nothing can justify this military action," he said. "Iraq posed no threat. Especially after a 10-year blockade, it was a weak country both militarily and economically."

Putin did not refer to Bush as his friend and a good politician, as he has done in recent weeks, but, in an apparent effort to protect Russia's budding partnership with the United States, he did not criticize Bush personally.

In Japan and South Korea, however, the threat of the North Korea crisis and the loyalty expected of allies prompted the governments to support the U.S. attack despite public opposition. Both had wavered on whether they would support an attack not sanctioned by the United Nations.

"It is in our best interest to support the United States," said South Korea's new president, Roh Moo Hyun, after an emergency meeting of his National Security Council. The Japanese prime minister, Junichiro Koizumi, said his government's support is the price of U.S. protection in case of conflict with North Korea. In a televised speech, Koizumi noted, "America has said clearly that any attack on Japan is an attack on the United States. . . . The Japanese people must not forget that this provides a strong deterrent against an attack on Japan."

In Islamabad, Pakistan, Foreign Minister Khurshid Mahmud Kasuri walked a fine line between offending public opinion, which is overwhelmingly opposed to the war, and offending the Bush administration.

"Pakistan deplores the initiation of military action against Iraq," Kasuri said. But he added, "We regret that President Saddam Hussein did not consider all options to save the Iraqi people from death and destruction."

The government's stance did not sit well with the hard-line Islamic parties that constitute Pakistan's main parliamentary opposition. They called for nationwide protests after midday prayers on Friday.

Israel, hit by 39 Scud missiles during the Persian Gulf War in 1991, recommended that all residents carry gas masks and many children lugged cardboard boxes containing their masks to school. The military placed its antimissile defense systems on highest alert, according to a senior military official, although officials have said they believe the diminished capability of the Iraqi military has reduced the threat of Scud attacks.

President Jacques Chirac of France expressed regret over the conflict in a television address and said it would have "serious consequences." But he did not criticize the United States by name, and emphasized the importance of avoiding civilian suffering. "I hope these operations are as fast as possible, with the least fatalities, and that they do not lead to a humanitarian catastrophe," Chirac said.

German Chancellor Gerhard Schroeder, Chirac's principal ally in Europe on the issue, took a similar tack. "The wrong decision was made. The logic of war won out over the chance of peace," Schroeder said in a television address. "But this is not the time to make accusations and to list faults. Our task must point to the future. The war has begun. It must be ended as quickly as possible. Hopefully, the victims in the civilian population will stay as low as possible."

Among U.S. allies in the war, Prime Minister Jose Maria Aznar of Spain said, "We have assumed our responsibilities. There were more comfortable options, but we don't want to pass on to the future risks that we should confront in the present."

Gloria Macapagal Arroyo, president of the Philippines, said, "The war in Iraq is a reality that we expected" and added, "The Philippines is part of the coalition of the willing."

Churches generally opposed the war, and the Vatican said it was "deeply pained" by it. Secretary of State Colin L. Powell gave the Vatican advance warning of the attack in a telephone call Monday, and Pope John Paul II was awakened at dawn this morning to be informed of the missile strike on Baghdad.

"The Holy See has learned with profound sorrow of the evolving of the most recent events in Iraq," spokesman Joaquin Navarro-Valls said in a statement.

"On one hand, it laments that the Iraqi government did not accept United Nations resolutions and the same appeal by the pope, who asked for the country's disarmament," he said. "On the other hand, it deplores the interruption of the path of negotiations, according to international law, for a peaceful solution to the Iraqi drama."

Rowan Williams, archbishop of Canterbury and spiritual leader of the world's 70 million Anglicans, said in a statement with David Hope, the archbishop of York, that the world had entered "dangerous new terrain."

Correspondents John Pomfret in Beijing, Doug Struck in Tokyo, Sharon LaFraniere in Moscow, DeNeen L. Brown in Toronto and John Lancaster in Islamabad contributed to this report.

Police fire water cannons to disperse antiwar protesters outside the U.S. Embassy in Brussels, where leaders of European Union nations were holding a summit to discuss postwar Iraq.