U.S. officials denied Powell changed plans because of protests against U.S. foreign policy that were dispersed when police hurled tear gas on Friday at about 1,000 demonstrators headed in the direction of the U.S. Embassy in Athens.

On Saturday Greek activists hoisted a massive banner saying "Powell Killer Go Home" on the Acropolis hillside towering over Athens to protest against his planned 24-hour visit.

"Secretary of State Colin Powell informed Greek Foreign Minister Petros Molyviatis that due to the press of business in Washington the secretary would not be able to travel to Athens to attend the closing ceremonies of the Olympic Games," State Department spokesman Richard Boucher said in a statement.

Boucher said Powell called Molyviatis on Friday and "expressed his congratulations to the government and people of Greece for hosting a spectacular, safe and successful Olympics."

The Greek government, which may have been embarrassed by Powell's cancellation, said he told Molyviatis he could not come because of "pressing obligations" and that the two agreed he would visit Greece in the first half of October.

The International Olympic Committee declined to comment on Powell's decision. But an organizer of protests in Athens said it was a victory for the anti-war movement.

"Of course, the cancellation was linked to our protests," Yiannis Sifakakis told Reuters. "This is a huge victory for the anti-war movement which protested by the thousands in the streets of Athens last night.

"It is very clear why he is not coming even if he is trying to come up with excuses. But whenever he should decide to come we will lay on the same welcome," Sifakakis said.

UNSPECIFIED DIFFICULTIES

A senior U.S. official hinted that Powell's trip might have caused unspecified difficulties for Greece, which has mounted a major security operation to keep the Olympics safe.

"The Greeks have done a terrific job with the Olympics and the last thing that we want to do is have complications with a trip that might detract from their success," said the official, who asked not to be named.

Asked what would keep Powell in Washington, State Department spokesman Kurtis Cooper said: "Among other things, there is much going on in Iraq, especially in Najaf, and in Sudan that requires the secretary close attention."

The situation in Najaf appeared calmer than it has been for weeks when Shi'ite fighters on Friday left the Imam Ali Mosque and began turning in their weapons after a peace agreement ended their bloody rebellion.

Sudan faces a U.N. deadline next week to defuse a humanitarian crisis in its western Darfur region or possibly face sanctions.

Washington accuses Khartoum-backed militias drawn from nomadic Arabs of ethnic cleansing against villagers who speak African languages in a crisis the United Nations estimates has killed some 50,000 people and left 1.2 million homeless.

On July 30 the U.N. Security Council gave Sudan 30 days to prosecute and disarm the militias accused of widespread killings, rape and uprooting villagers. The council deliberates on Sudan's efforts next week but no major action is expected.