In another sign of growing tensions with the United States, Pakistan is threatening to turn over to Iran six members of a tribal militant group Iran claims are "spies" for the CIA.

The group, Jundullah, operates in Baluchistan on both sides of the border between Iran and Pakistan and has carried out a number of violent attacks on Iranian army facilities and officers inside the country.

The CIA has denied any direct ties with the group, but U.S. officials tell ABC News U.S. intelligence officers frequently meet and advise Jundullah leaders, and current and former intelligence officers are working to prevent the men from being sent to Iran.

The six Jundullah members were taken into custody by Pakistani authorities last week, and the Iranian Mehr News Agency reported Pakistan would soon extradite the men to Iran, where they would likely be put on trial as spies and face execution.

Officials said the group's leader, Abdel Malik Regi, was not among those arrested by Pakistan.

U.S. intelligence officials say they are aware of the developments with the Jundullah members and are said to be trying to block the extradition. In addition to causing turmoil in Iran, the officials say the group has been helpful in tracking al Qaeda figures trying to move through the Baluchistan region to Iran.

"The new Pakistan leaders have said they are going to do it, but they are saying a lot of things and trying to make a lot of deals," said one U.S. official. "If they are seeking stability inside the country, why would they want to inflame people in this region?" the official asked.

Iranian officials claimed this week that the U.S. had "a hand" in an April 12 bomb attack at a mosque in Shiraz that killed 14 people, according to Mehr News Agency, quoting Iranian Intelligence Minister Gholam-Hossein Mohseni Ejei.

"The U.S. is behind many events in Iran and the region with the aim of bringing insecurity," the intelligence minister reportedly said. "We have proper documentations in this regard," the minister told the news agency's reporters.

A senior U.S. official said Iran's claims "are nonsense, ludicrous."

The capture of the Jundullah members is seen by intelligence sources in the region as another indication that Pakistan's new government is distancing itself from the U.S. and U.S. intelligence operations in the country.

Other such steps by Pakistan in recent days include an accord between Pakistan's government and militant tribal leaders in the country's Swat Valley region where Taliban figures are believed to be hiding. Increasingly, U.S. sources say, Pakistan is effectively handcuffing U.S. ground efforts against al Qaeda in the border region and emboldening the Taliban.