The state department is warning Americans to avoid non-essential travel to Pakistan as protests over an anti-Islam video made in the US grow and turn violent.
The department issued an alert on Thursday.
It's stepping up existing advice for Americans to be aware of the risks of travel to Pakistan.
It says protests and demonstrations, some targeting US interests, are likely to continue.
The warning comes as hundreds of Pakistanis angry at the film clash with police in the capital, Islamabad.
A crowd of more than 1,000 people tried to make their way to the US Embassy inside a guarded enclave that houses embassies and government offices.
Riot police used tear gas and batons to keep stone-throwing demonstrators away.