Her aides said that she will personally deliver a blunt message from the Obama administration that Pakistan must step up its counter-terror efforts.

Earlier, in Kabul she called for a new partnership between the US, Afghanistan and Pakistan to fight militants.

She said Pakistan "must be part of the solution" to the Afghan conflict.

Mrs Clinton is due to be joined in Islamabad by CIA chief David Petraeus and Chairman of the Joint Chiefs of Staff Gen Martin Dempsey.

Mrs Clinton's visit to Pakistan comes at a time when relations between Washington and Islamabad are at their lowest point since the US-led invasion of Afghanistan in 2001.

Washington has for many years urged Islamabad to deal with militants in the North Waziristan tribal area - especially the Haqqani network - who have been blamed for a series of recent attacks in Afghanistan.

The verbal and military assault waged by the US against the network has intensified in recent months and comes amid heightened tension between the US-led coalition in Afghanistan and the Pakistani government.

Islamabad for its part was angered by the killing of Osama Bin Laden - apparently without its knowledge - by US special forces in May and is concerned about repeated US drone strikes against militant targets in its north-west.

Relations between the two countries were also strained after the killing of two Pakistanis in January by CIA contractor Raymond Davis in the city of Lahore.