(Updates with Rice quotes, U.S. departures from Belgrade)

WASHINGTON, Feb 22 (Reuters) - The United States holds the Serbian government responsible for the attack on the U.S. embassy in Belgrade this week by rioters angry over Kosovo's secession, Secretary of State Condoleezza Rice said on Friday.

Speaking to reporters, Rice said the Serbian government had failed in its obligation to protect the U.S. Embassy, as well as a number of other embassies, from attack on Thursday.

"They had an obligation to protect diplomatic missions, and, from what we can tell, the police presence was either inadequate or unresponsive at the time," she said.

"We do hold the Serb government responsible. We've made that very clear," Rice said, adding, "We don't expect that to happen again." The United States protested against the attack on Thursday to Serbian authorities.

Earlier on Friday the State Department approved a request from the U.S. ambassador in Belgrade for family members and non-emergency personnel to be allowed to leave the Serbian capital until security there improves.

A U.S. official said 90 Americans, including officials and their families, were departing Belgrade for now; 50 "official Americans" will continue working in Belgrade.

A charred body was found in the embassy after the protesters smashed their way in and set it on fire, but U.S. officials believe it is that of a protester. There were 14 Americans in the building during the attack, but all were safe. Rice said the "important parts of the facility" were secure.

She said the United States wanted to be a friend to Serbia, and only maintained a military presence with some 17,000 NATO forces in Kosovo because of continued tensions between minority Serbs and Kosovo's ethnic Albanian majority.

Kosovo's Albanian-majority population has been under U.N. stewardship since 1999, when NATO intervened to halt the killing of civilians in a Serb crackdown on a separatist insurgency.

"I don't think anyone will be happier than the American president on the day that Kosovo is capable of having the kind of security forces that can take care of its people and contribute to regional stability," she said.

Serbia had to look to the future, Rice said, and resolving Kosovo's status should let the Balkans begin to put its "terrible history" behind it. Undersecretary of State Nicholas Burns, told reporters separately that "there is a feeling of real anger" among U.S. diplomats over the embassy attack.

Burns added, "We've had a lot of public advice from the Russians today, most of it very bad." He did not elaborate. Russia, Serbia's ally, said earlier that Western states should have anticipated the backlash over Kosovo, seen by Serbs as the nation's heartland. (Editing by Patricia Zengerle)

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