The United States has pulled its ambassador out of Syria because of concerns for his safety.
The State Department says Robert Ford has become the subject of an incitement campaign by the Syrian regime.
The BBC reports that the Syrian ambassador to Washington has been called back to Damascus for consultations in response.
Mr Ford and colleagues were pelted with eggs and tomatoes when visiting an opposition figure in Syria last month.
He was then briefly trapped in his office by pro-Assad demonstrators.