Secretary of State Hillary Clinton will visit Pakistan soon, but her travel dates cannot be revealed due to security reasons, the US State department has said.

"We are not going to announce specific dates for her travel for security reasons," assistant secretary of State for Public Affairs PJ Crowley said.

Clinton has indicated "many, many times" that she looks forward to travelling to Pakistan on her maiden visit this fall, he said.

Special US representative for Pakistan and Afghanistan Richard Holbrooke said, "There are security constraints on how we discuss this (Clinton's trip to Pakistan).

"There are already some reports out of Islamabad about what the secretary is going to do and when she's arriving. That's all speculation."

Holbrooke said that if speculations surrounding Clinton's trip were found to be even remotely closer to reality, the plan would be changed or rescheduled.

"If the speculation (in Pakistan) is too well informed, it will affect the content of the trip," he said.

He said Clinton will hold discussion with Pakistani leaders, military commanders and members of the civil society, and meet as many people as she can in a limited period of time "within the limits of a very, very dramatic situation going on (in Pakistan)".