An American was held for questioning in Pakistan on Tuesday after security officials at the airport in northwestern Peshawar discovered bullets in his luggage, police said, the latest likely irritant in ties between the two countries.

The American was due to fly from Peshawar to the capital Islamabad, said Tahir Ayub, a senior police superintendent.

He has been detained at the airport and is under interrogation, Ayub told Reuters. We are in contact with the foreign office in Islamabad to check about his background and tell us if he has diplomatic immunity.

Ayub said a pistol and 12 magazine rounds had been recovered from the man's luggage, while another police officer said security officials had only found bullets.

A U.S. official in Islamabad said the embassy was looking into the details of the reports.

The detention is likely to revive memories of Raymond Davis, an American CIA contractor who shot and killed two Pakistanis in the eastern city of Lahore in January 2011.

A third Pakistani died when he was hit by an embassy vehicle racing to extract Davis from the scene where an angry mob had gathered.

After initial confusion, the U.S. embassy in Islamabad said Davis had diplomatic immunity, which Pakistan refused to recognise. Davis spent almost two months in jail before being released after the payment of compensation to the families of the two men killed.

The incident was a major blow to the relationship between the United States and Pakistan, a key ally in the war on terror.

Ties were just beginning to thaw when U.S. commandos killed al Qaeda leader Osama bin Laden in a Pakistani military town on May 2 in a secret raid which infuriated Islamabad.

(Reporting by Faris Ali and Jibran Ahmad in PESHAWAR and Chris Allbritton in ISLAMABAD; Writing by Serena Chaudhry; Editing by Nick Macfie)