Pakistani officials say a suspected U.S. drone missile strike killed at least six militants Wednesday in a tribal district near the Afghan border.

The attack struck an area of North Waziristan that is a stronghold of an Afghan Taliban faction called the Haqqani network.

Authorities say a similar strike last week killed, Mohammad Haqqani, the son of the group's leader, Jalaluddin Haqqani.

There has been a recent increase in U.S. drone missile attacks targeting Taliban and al-Qaida linked militants in the region.

Also in North Waziristan, Pakistani officials say militants have beheaded at least three men accused of being spies for the United States.

Officials say the men's bodies were found Wednesday.  Notes placed nearby warned other people they will meet the same fate if they engage in espionage.

Militants in recent years have killed a number of people they suspect of spying for the Pakistani or U.S. governments.

The attacks come as the head of the U.S. Federal Bureau of Investigation visits Islamabad for talks with Pakistani officials.

FBI Director Robert Mueller has said the greatest terror threat to the United States comes from militants in the border regions between Pakistan and Afghanistan.

On Tuesday, U.S. General David Petraeus credited Pakistani intelligence operations for the recent capture of several Afghan Taliban commanders.

They include the Taliban's second-in-command, Mullah Abdul Ghani Baradar, who was arrested in a joint operation with U.S. agents.  Officials say the operation highlighted increased cooperation between U.S. and Pakistani intelligence agencies.

Some information for this report was provided by AP and Reuters.