BELGRADE, Serbia (CNN) -- The U.S. Embassy in Belgrade is evacuating all nonessential personnel following Thursday's attack on the building by a crowd of protesters, a spokesman for the embassy told CNN Friday.
Serbian riot police stand in front of the damaged U.S. Embassy in Belgrade on Friday.
The U.S. ambassador, Cameron Munter, is staying, officials said.
The embassy was closed Friday, and a handful of riot police holding shields stood outside the building, its outer walls blackened from fires set the night before and some of its windows smashed.
It will remain closed until Monday or Tuesday so officials can assess the damage, said Bill Wanlund, the embassy's spokesman.
He said embassy staff were still in a heightened state of alert but there were no specific threats against any staff members.
The United States has warned the Serbian government that it has a responsibility to protect its assets.
A top U.S. diplomat was asked during an interview on CNN if the Serbian government "gets" the warning.
"They'd better get it, because they have a fundamental responsibility to protect our diplomats and our embassy and to protect American citizens," said Undersecretary of State for Political Affairs R. Nicholas Burns. "What happened yesterday in Belgrade was absolutely reprehensible." Watch Burns' angry comments on Belgrade attack »
Thursday's violence erupted after demonstrations by thousands of Serbs against Kosovo's declaration of independence. The anger directed against the United States and other countries for recognizing the breakaway province as a nation sparked attacks on Western embassies and shops by hundreds of people.
Burns said there was an "insufficient" number of security people guarding the U.S. Embassy at a demonstration everyone knew would take place. He said security "melted away" as "the mob attacked our embassy."
"This kind of thing should not happen in a civilized country. It doesn't happen in the United States of America. It doesn't happen in most world capitals. So the Serb government needs to reflect seriously about the responsibility it has under the Vienna Convention," he said.
Burns, the third highest ranking diplomat in the State Department, said he told the Serbian prime minister, Vojislav Kostunica, and his government that the U.S. "would hold them personally responsible for the safety of our people."
"They assured me that they would have adequate security on the ground today and for every day to come. We will hold them to that commitment," Burns said.
Demonstrators only managed to break into one U.S. embassy building, which Wanlund said was rarely used by staff. He said the protesters didn't manage to get any documents or embassy materials.
Only Marines and security guards were present at the embassy when the angry mob of about 100 approached the walls.
In addition to the U.S. Embassy, the protesters attacked other Western interests including the embassies of Britain and Germany, as well as a McDonald's restaurant and a Nike shop.
"One might understand the emotion, but not the violence, and that's what the Serb government needs to remember," Burns said.
Burns, who is stepping down in March, has long been involved in trying to resolve tensions in the former Yugoslavia. The situation was complicated by Sunday's unilateral declaration of independence by Serbia's predominantly Albanian region of Kosovo. Kosovo is revered historically by Orthodox Christian Serbs but also is claimed as separate and distinct by its ethnic Muslim Albanians.
The wisdom of recognizing Kosovo independence has been questioned by many observers, who say the United States won't recognize other unilateral declarations of independence.
Some opponents of Kosovo's independence say recognition is a bad precedent if it's unilateral and not done in a bilateral, diplomatic setting. They say it will give others the incentive to stage their own breakaway nations.
Burns said every situation has its unique set of circumstances, as does Kosovo, which was the victim of ethnic cleansing policies by the Slobodan Milosevic regime in 1999.
NATO troops fought Serbia in an air war then and pushed Serbian forces out of the region. Since then Kosovo has been run by the United Nations and with security supplied by NATO forces. E-mail to a friend