The US Embassy on Thursday issued an emergency message asking American citizens in Pakistan to take precautions for the next two weeks though it did not give any reasons for the alert.
"This security message from the US Embassy in Islamabad, Pakistan alerts US citizens to travel restrictions for US Embassy staff during the next two weeks," said the message posted on the Embassy's website.
The message said the US Embassy had restricted its employees from going to restaurants and markets in Islamabad during April 27-May 5 due to "security concerns".
It added: "We recommend that US citizens in Islamabad during this period take similar precautions."
"Also, based on the current security conditions and a significant increase in the level of sectarian violence in northern Pakistan, the US Embassy has prohibited its employees from taking personal trips to the Gilgit/Skardu area until further notice," the message said.
The US Embassy "continues to recommend that US citizens defer all non-essential travel to Pakistan," the message further said.
The mission asked Americans to refer to the US Department of State's current travel warning for Pakistan and reiterated its advice to all US citizens to "take measures for their safety and security at all times, including practicing good situational awareness, avoiding of crowds, and maintaining a low profile".
It reminded US citizens that "even peaceful protests may become violent" and advised them to avoid protests.
"US citizens should vary times and routes for all required travel. US citizens should ensure their travel documents and visas are valid at all times," it added.
Pakistan has witnessed a sharp increase in anti-American sentiments following a campaign of drone attacks in the tribal belt bordering Afghanistan, the unilateral military raid that killed Osama bin Laden in May and a cross-border NATO air strike that left 24 Pakistani soldiers dead in November.
The two countries are currently negotiating new terms of engagement for the resumption of cooperation in key areas like counter-terrorism.