PESHAWAR, Pakistan (AFP) - At least 23 Pakistani soldiers were killed on Saturday when their bus plunged into a ravine on the main Pakistan-China highway in the mountainous northern region, officials said.

"According to initial information, 23 soldiers died in a road accident when their bus plunged into a ravine on the Karakoram Highway," said a senior military official.

The military said 27 people were on board the bus including 25 soldiers heading home on leave and a civilian driver and cleaner.

The soldiers belonged to a battalion of the Northern Light Infantry (NLI) and were deployed to the picturesque Swat valley, which was cleared of Taliban militants in 2009.

A local administration official said they had dispatched teams to the remote accident site.

"They were all proceeding on leave from Swat to Gilgit," the military official said.

The journey in the mountainous northern districts is quite difficult and soldiers and civilians prefer to travel in groups.