The Pakistani Taliban are claiming responsibility for an attack on NATO supply trucks that killed four people in the country's northwest.

Around 15 militants on Monday fired rockets at the trucks as they traveled in the Khyber tribal region on their way to Afghanistan. Because of such attacks, the U.S. has for years been reducing its use of Pakistani land routes to get supplies to troops in Afghanistan.

Late Monday, Pakistani Taliban spokesman Ahsanullah Ahsan said more such attacks were planned. He also warned the new government in Pakistan's northwestern province to close the supply route.

The ruling party there is that of former cricket star Imran Khan, and it adamantly opposes U.S. drone strikes in Pakistan. It has hinted at preventing the NATO supply trucks from crossing its territory.