Last week, 108 people were massacred in the rural district of Houla.
WASHINGTON -- The Obama administration is giving Syria's most senior envoy in Washington 72 hours to leave the U.S.
At least eight other Western countries also are expelling Syrian diplomats following last week's massacre of more than 100 Syrian civilians in Houla.
Meanwhile, activists say Syrian troops are shelling restive suburbs of Damascus and rebel-held areas in the central city of Homs.
The Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees did not have any details of casualties caused by the bombardment in Homs city and the suburb Douma.
The rural district of Houla, where 108 people were massacred last week, is in the province of Homs.
The Syrian government has said it will conclude its own investigation into the killings. It is not clear whether the results will be made public.