Militants in northwest Pakistan set off a bomb while targeting a temporary military camp with rockets and guns, in an incident that killed at least three troops, security officials said on Friday, but there was no immediate claim of responsibility.

The violence comes after Pakistan declared a new offensive against militants following a resurgence of attacks in recent months, such as a February mosque bombing that killed more than 100.

Troops engaged the attackers for several hours from Thursday night in the district of Lakki Marwat, near a rugged tribal area bordering Afghanistan, two officials told Reuters, on condition of anonymity as they were not authorised to provide information.

At least three troops and several of the militants died as a result, they added. The soldiers had been on their way to take up new posts at a nearby military base.

The army’s public relations wing gave no details of the incident and did not immediately respond to a request for comment.

A report made by a Pakistani intelligence agency to government officials, which was seen by Reuters, identified a new, little-known militant group, the Tehreek-e-Jihad Pakistan, as being involved in the attack.

Reuters could not immediately confirm the report.

The tribal region has long been home to Islamist militants, including the Tehreek-e-Taliban Pakistan, widely known as the Pakistani Taliban, which is an umbrella group of several Sunni militant outfits.

The local Taliban have been waging a war on the state in a bid to overthrow the government and replace it with their own harsh system of Islamic governance.

Pakistan’s military has launched several operations in the area, dismantling the militants’ infrastructure and networks, forcing their leaders to flee to neighbouring Afghanistan.