Pakistan on Thursday stepped up security measures around US diplomatic missions, following attacks on American consulates and embassies in Libya, Egypt and Yemen over an anti-Islam film.
A mob stormed the US consulate in the eastern Libyan city of Benghazi on Tuesday, killing US ambassador Christopher Stevens and several other staff members.
There were also anti-US protests in Egypt's capital Cairo and on Thursday a crowd stormed the American embassy complex in Yemeni capital Sanaa before being driven out by police.
"We have beefed up the security for the possible threats to the US embassy," Khurram Rasheed, a senior police official responsible for diplomats' security in Islamabad, told AFP.
"We expect some protests against the embassy tomorrow and we are preparing to handle that."
The US embassy in Islamabad lies inside the city's heavily-fortified diplomatic enclave, and Rasheed said the entrance would be closed and extra security forces deployed.
In the eastern city of Lahore, police said they have issued an alert to protect the US consulate.
"The security is already tight but we have issued an alert to be careful for any urgent situation," Abdul Ghaffar Qaisrani, senior police official responsible for security, told AFP.
"We are also gathering information (on) whether some organisations are planning to organise some protests. In that case, we will take further measures to protect the US consulate."
The low-budget movie, entitled "Innocence of Muslims", which has sparked fury across the Muslim world, portrays followers of the faith as immoral and gratuitously violent.
It pokes fun at the Prophet Mohammed and touches on themes of paedophilia and homosexuality, while showing him sleeping with women and talking about killing children.
Foreign Minister Hina Rabbani Khar criticised the film.
"We have always promoted inter-faith harmony but desecration of any type is always condemned by Pakistan and we are very, very strongly condemning," she said when asked about her government's reaction to the disputed film.
In the northwestern city of Peshawar, where anti-US sentiments run high and a car bomb attack on a US consulate vehicle killed two people on September 3, authorities said they were "cautious" about the developing situation.
The patrolling of police around the consulate in the southern port city Karachi was also stepped up.
Ties between Islamabad and Washington have been rocky for years, and are only just beginning to pick up after nosediving last year following the secret raid that killed Osama bin Laden and an air raid that accidentally killed 24 Pakistani troops.