Pakistani authorities briefly questioned three American diplomats on Monday in the city of Peshawar after weapons were found in their vehicles, police said.

The diplomats, accompanied by three Pakistani nationals, were stopped at a routine checkpoint where they refused to have their vehicles searched, police said.

When police checked anyway, they said they found several rifles, pistols and ammunition. The Pakistanis were charged with illegal possession of weapons, police said.

A U.S. embassy official said: "These officials were returning from a visit to Malakand University where they were preparing for an English education event for underprivileged children. They had all proper permissions but were stopped when returning to Peshawar."

Relations between the United States and Pakistan have sunk to their lowest in years over a series of events, including the recent imprisonment of the Pakistani doctor who helped the CIA hunt down Osama bin Laden.

Police said the Americans also had been questioned because they left Peshawar on a trip and returned without proper documents.

Last year, CIA contractor Raymond Davis killed two Pakistanis in the eastern city of Lahore, straining ties between Washington and Islamabad.

Washington says he acted in self defense. REUTERS

Davis was acquitted of murder and allowed to leave Pakistan after a $2.3 million payment was made to the men's families.