The U.S. Embassy in Islamabad says it has restricted its staff from going to restaurants and markets in Pakistan's capital for several days around the anniversary of Osama bin Laden's death.
The Al-Qaeda founder was killed in a raid by U.S. Special Forces in Pakistan's garrison town of Abbottabad on May 2, 2011.
There are concerns militants may try to mark the anniversary with an attack.
An "emergency message" on the U.S. Embassy's website recommends U.S. citizens in Islamabad take similar precautions.
A U.S. official, speaking on condition of anonymity, said the warning was issued in response to information about a specific threat.
But Pakistan's Deputy Interior Minister Imtiaz Safdar Warraich said he did not have information about any threat.
With reporting by AFP