Bus drivers in northwest Pakistan have begun removing audio and video equipment from their vehicles after Taliban militants threatened attacks against those who played music or movies for their passengers, an industry official said Tuesday.

Transport workers in the town of Mardan received letters this week from militants saying that buses offering such entertainment were guilty of spreading "vulgarity and obscenity," Walid Mir, general secretary of the town's transport union, told The Associated Press.

The militants said they would check the buses and that attacks would be carried out against vehicles that still had audio and video equipment — prompting union members to act quickly, Mir said.

The Taliban letter complained that traveling in buses that provide audiovisual entertainment was a "source of mental agony for pious people," according to a text obtained by AP.

"It is obligatory on us to stop such violations. We request you to remove the vulgar systems ... otherwise ... bombers are ready," the letter said.

Mardan lies in the Northwest Frontier Province just outside Pakistan's volatile tribal belt where extremists among the Taliban, Al Qaeda and local groups are waging a violent campaign against authorities in a bid to impose their strict interpretation of Islam.

Elsewhere in northwest Pakistan, extremists have targeted girls' schools, police posts and other symbols of authority.

In Afghanistan, the Taliban regime that was forced from power in late 2001 banned art, secular music and television, vandalized the national museum and destroyed artwork or statues deemed idolatrous or anti-Muslim.

Local police said they had no knowledge of the threat.

"Certainly, we can look into it if we receive a complaint," Mardan police chief Syed Akhtar Ali Shah said.

Mir said the transport companies had no plans to make a report.

"We did not report it to police because it is a matter of human lives. What can the police can do? It involves the lives of hundreds of passengers, and we do not want to put them in danger," Mir said.