A top White House official said Sunday the United States has decided to suspend $800 million in military aid to Pakistan.

White House Chief of Staff William Daley told ABC's This Week that although U.S.-Pakistani ties are difficult and complex right now, they must be made to work over time. He said Pakistan has been an important ally in the fight against terrorism, but it has taken some steps that have given Washington reason to pause some of the military aid. He did not elaborate.

U.S. officials have been quoted as saying the move is a response to Pakistan's decision to expel American military trainers and put limits on visas for U.S. personnel.

Analysts say the suspension also is aimed at pressuring Pakistan's army to do more to cooperate with the U.S. to fight militants.

Ties between Washington and Islamabad have been frayed since the raid by U.S. special forces that killed al-Qaida leader Osama bin Laden in northern Pakistan on May 2.

Last week, Admiral Mullen sparked a controversy when he commented on the murder of Pakistani journalist Saleem Shahzad, who was beaten to death in May. Mullen said that while he could not tie the killing to any specific Pakistani agency, he had not seen any evidence to counter reports that the government approved the murder.

Islamabad denounced his comments, calling them “extremely irresponsible and unfortunate.”