PESHAWAR, Pakistan (AP) — A militant faction in Pakistan that split years ago from the Pakistani Taliban has returned and rejoined the insurgents, a Taliban spokesman said Monday.

In a statement, spokesman Mohammad Khurasani, says top leaders and fighters from the splinter faction — which later evolved into two separate militant groups — were welcomed at a recent ceremony after they decided to “merge back” with the Taliban.

The Pakistani Taliban, also known as Tehrik-e-Taliban Pakistan, or TTP, are separate from the Afghan Taliban.

One of the militant groups, Jamaat-ul-Ahrar, was formed in 2014 by Umar Khalid Khurasani when it split from the TTP. The other group, Hizbul Ahrar, was first established in Afghanistan’s eastern Nangarhar province.

The merger of the two militant groups, which have been blamed for several deadly attacks in Pakistan, was seen as a boost for the Pakistani Taliban.

The development comes after a recently released U.N. report suggested that more than 6,000 Pakistani insurgents were hiding in neighboring Afghanistan — most of them belonging to militant groups behind attacks on Pakistani military and civilian targets.

The Pakistani Taliban claimed responsibility for one of the most horrific attacks in the country — the 2014 attack on a military school in the city of Peshawar when 140 people were killed, mostly students at the school — some as young as 5.