DERA ISMAIL KHAN, Pakistan (Reuters) - Taliban gunmen opened fire on a police vehicle and killed four officers in northwestern Pakistan on Tuesday, officials said, in a region once riven by militant violence but since cleared following military crackdowns.

The ambush, claimed by the Hizbul Ahrar, a splinter group of the Pakistani Taliban, was the first major attack in the Dera Ismail Khan district of Khyber Pakhtunkhwa since a suicide blast killed a candidate in the lead-up to the July general election.

“The officers were out patrolling the area when six to seven people who were waiting for them opened fire on their vehicle,” senior police official Mohammad Iqbal told Reuters.

“The assailants were seated at a local tea stall and opened fire when the police vehicle approached.”

Iqbal said four police were killed and three people were wounded. Among the wounded is a senior police officer said to be in critical condition.

“Today Hizbul Ahrar target killers ... made a police vehicle their target,” the group’s spokesman, Aziz Yousafzai, said in a statement sent to Reuters via Whatsapp.

Dera Ismail Khan is on the edge of Pakistan’s former tribal areas that border Afghanistan, large swaths of which were once controlled by the Pakistani Taliban before military operations in 2009 and 2014 ended militant control of the region.