U.S. officials say Washington is considering closing its embassy in Damascus due to what it considers the worsening security situation in the Syrian capital.
The U.S. threat came as the White House said it believed Syrian President Bashar Assad no longer had full control over the country.
At least six people were killed in Syria on January 20, two days before the Arab League decides whether to keep monitors there despite their failure to halt bloodshed.
Security men were deployed in restive towns and cities to counter protests against Assad while dozens of his supporters demonstrated in Damascus.
Reuters