Chairman of the Joint Chiefs of Staff Michael Mullen - AFP File Photo

ISLAMABAD: The top US military officer is visiting Pakistan at a time of tensions over America's role in the region.

The US Embassy says Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, will spend Wednesday and Thursday meeting with Pakistani leaders.

Admiral Mike Mullen's trip follows a visit to Afghanistan a day earlier in which he told reporters he would raise ongoing concerns with Pakistan army chief General Ashfaq Kayani, according to the Joint Chiefs of Staff website.

Mullen praised cooperation between US and Pakistani troops in working jointly to combat the militant Haqqani network who target NATO forces in the Afghan east, but acknowledged “strain” caused by the insurgents' ties with ISI.

“Haqqani is having a much more difficult time now,” Mullen told reporters, according to an article on the website.

“All that said, we're still working through the (Pakistani) military support, the way through the relationships the (Pakistani intelligence agency) has with the Haqqani network, and the strain that creates.” The Haqqani network is an al Qaeda-allied outfit run by Afghan warlord Sirajuddin Haqqani and based in Pakistan's North Waziristan tribal district.

The group has been blamed for some of the deadliest anti-US attacks in Afghanistan, including a suicide attack at a US base in Khost in 2009 that killed seven CIA operatives.

The commander of coalition forces for the eastern region of Afghanistan, Major General John Campbell, told reporters during Mullen's visit that efforts to work with Pakistan to counter the Haqqani threat had improved.

There were complementary operations either side of the border, but he acknowledged: “I don't know at what level they are tied in to the ISI.”

Mullen is a frequent visitor to Pakistan, and reportedly has a good relationship with Gen. Kayani.

The United States needs Pakistan's cooperation to help end the war in Afghanistan.

But tensions between the two allies have spiked this year after an American CIA employee shot and killed two Pakistanis he said were trying to rob him.

A March missile strike ostensibly targeting the Taliban also angered Kayani, who said dozens of innocent tribesmen were killed.