"The United States strongly condemns the attack on the Swedish Embassy in Baghdad in the early hours of July 20," said State Department spokesman Matthew Miller.

"It is unacceptable that Iraqi Security Forces did not act to prevent protestors from breaching the Swedish Embassy compound for a second time and damaging it," he said.

Early Thursday followers of powerful Shiite Muslim cleric and political leader Moqtada Sadr led the attack on the embassy compound, setting fire to buildings.

The attack came ahead of a planned Koran-burning protest in Stockholm, the second in less than a month, which the Iraqi government condemned.

Miller said in a statement that freedom to protest is an essential part of democracy.

"But what occurred last night was an unlawful act of violence," he said of the attack.

"Foreign missions should not be targets of violence," he said.

Miller called on the Iraqi government to live up to its obligations under international law to protect foreign diplomatic missions.