A senior U.S. official is heading to Pakistan to press the country for support on fighting the Haqqani network blamed for recent attacks on the U.S. embassy in Afghanistan, State Department said on Friday.

State Department spokesperson Victoria Nuland told reporters that U.S. special envoy for Pakistan and Afghanistan Marc Grossman, who is leaving on Friday evening, will visit Afghanistan, Pakistan and some neighboring countries.

Nuland said the U.S. continues to believe the most urgent challenge between the U.S. and Pakistan on the counter terrorism front is to "tackle the Haqqani network."

"I think what's important in this case is that we continue to have very clear and candid conversations among all of the principals with their Pakistani interlocutors," she said, adding that Grossman's trip to the region is meant to "continue those conversations."

According to Nuland, Grossman's mission also includes persuading Afghanistan, who has concerns and reservations about the three-way talks among the U.S., Afghanistan and Pakistan on counter terrorism effort, to continue take part in the platform.

U.S.-Pakistani relations has been deteriorating since a secret U.S. commando mission killed al-Qaida leader Osama bin Laden in Pakistan in May without the knowledge from Islamabad.

The bilateral ties have been further damaged after Mike Mullen, chairman of U.S. Joint Chief of Staff, accused publicly last week the Haqqani network of being "a veritable arm" of Pakistan's intelligence service.

Pakistan reacted furiously to Mullen's statement, warning that the U.S. might lose an ally of the war on terror, While America has been urging Pakistan to cut links with the Haqqani network and eliminate its safe havens within its borders.