QUETTA, Pakistan (AP) — A double landmine blast killed one person and wounded at least 18 Thursday in Pakistan’s southwest, a police officer said.

The first landmine exploded when a truck was passing through a valley in coal-rich Duki district, Baluchistan province. The second detonated when counter-terrorism officials and civilians were examining the initial blast site, said district police officer Asif Haleem.

No one immediately claimed responsibility for the blast. But Baluch separatist groups have previously struck security personnel or infrastructure in the southwest.

They initially wanted a greater share of provincial resources, but later initiated an insurgency for independence from the central government.

Also Thursday, an Islamabad-based think tank said that militant assaults killed 70 people nationwide in April, mostly in northwest Khyber Pakhtunkhwa province.

The Pakistan Institute for Conflict and Security Studies also said the country experienced 323 militant attacks in the first four months of the year, resulting in 324 deaths.

A report issued in January by another think tank, the Pak Institute for Peace Studies, said there were 306 attacks last year, killing 693 people.