The U.S. embassy in Syria's capital has issued a warning to Americans in the country to be alert following a raid on eastern Syria that Damascus blames on U.S. forces.
The embassy says "unforeseen events" could prompt officials to close the embassy to the public indefinitely.
Syria has protested to the United Nations about Sunday's deadly helicopter raid.
In a letter to U.N. Secretary-General Ban Ki-moon released Tuesday, Syria urged U.N. member states to prevent a repeat of the attack, calling it a serious violation of Syria's sovereignty.
Syria's letter also says the U.N. Security Council should take action against those responsible for the raid, saying it killed eight Syrian civilians, including children. The identity of the casualties has not been independently verified.
Syria's government ordered the closure of an American school and a U.S. cultural center in Damascus on Tuesday in apparent retaliation for the helicopter assault.
The Bush administration has refused to confirm or deny carrying out the attack.
But, U.S. officials, speaking anonymously, say the operation appears to have killed al-Qaida leader Abu Ghadiyah who smuggled weapons and foreign fighters into Iraq.
Iraqi government spokesman Ali al-Dabbagh criticized the attack Tuesday, saying his country "rejects" the operation and does not want its territory to be used for attacks on neighboring countries.
Al-Dabbagh also called on Damascus to crack down on insurgents who use Syria as a base to train and launch attacks on Iraq. Baghdad has said that Sunday's helicopter raid targeted such an area.
Syria expressed apparent displeasure with Iraq's reaction, postponing a meeting of Syrian and Iraqi officials planned for November in Baghdad.
Some information for this report was provided by AP and Reuters.