The Syrian government has ordered the closure of an American school and a US cultural centre in Damascus, in response to a US military raid inside its border with Iraq on Sunday.
Syria says eight civilians, including children, were killed in the assault - the first confirmed action of its kind by US military forces inside Syrian territory.
Syrian ministers have described the incident as a "terrorist aggression".
A US official says the raid targeted foreign fighters who infiltrate Iraq.
Syria is on a US list of states that support terrorism, and is under US trade sanctions over its support for Hamas and Hizbollah.
Earlier this month, General David Petraeus, the former US commander in Iraq, said the flow of fighters from Syria had fallen to 10 or 20 a month from a peak of 160.
