KABUL, Afghanistan (AP) — A senior Taliban figure resigned Tuesday in the latest fallout from the death of longtime leader Mullah Mohammad Omar, which has triggered a succession dispute and revealed growing rifts within the two-decade-old Afghan insurgent group.

Mohammad Tayab Agha, head of the Taliban’s political office, said in a statement that the movement had made a “historic mistake” by concealing Mullah Omar’s death and by choosing his successor outside of Afghanistan. The Taliban confirmed Mullah Omar’s death last week after Afghan authorities said he had died in a Pakistani hospital more than two years ago.

Mullah Akhtar Mansoor, who had served as Mullah Omar’s deputy, was chosen to succeed him by the group’s seven-member Supreme Council, meeting in the Pakistani city of Quetta. Mullah Omar’s relatives have rejected the decision, saying the new leader was chosen by a small clique of loyalists, and called for a wider vote.

Agha’s statement, which was confirmed by a current and a former member of the Taliban, appeared to reflect growing anger at Pakistan, which has long had influence over the group and played a key role in bringing them to the first round of official peace talks last month.

The Taliban are believed to be split over whether to pursue the negotiations or continue their 14-year insurgency now that U.S. and NATO troops have transitioned to a supporting role. The peace talks were indefinitely postponed after the announcement of Mullah Omar’s death.

Agha said the “appointment of every leader which has taken place outside the country has brought very bad repercussions for the oppressed Afghan nation.” He urged Taliban members living abroad to return to Afghanistan and “preserve their independence,” an apparent reference to Pakistan, where the Taliban’s leadership has long been based.

His resignation was confirmed by Waheed Muzhda, who was an official in the Taliban government in the 1990s. Agha was based in Qatar, where the Taliban has an unofficial office. Muzhda said at least one other member of the office had also resigned.

Around 200 high-ranking Taliban members meanwhile met in the Pakistani city of Quetta on Tuesday with Mullah Omar’s brother and son, said Mullah Hameedullah, a member of the Taliban’s Unity Council, which works to resolve internal disputes.

“We discussed the problems of both sides and in the end Mullah Omar’s family gave authority to the Unity Council that whatever decision they take they will agree to it and accept it,” Mullah Hameedullah told The Associated Press. He said the council would next meet with Mullah Mansoor. Mullah Omar’s son, Mullah Yaqub, confirmed he had attended the meeting but gave no further details.

The Taliban, meanwhile, issued another statement Tuesday urging followers to disregard “enemy propaganda” about internal fractures and to unite behind Mullah Mansoor. The statement, signed by spokesmen Zabihullah Mujahid and Qari Yusouf Ahmadi, called on supporters to “help write messages and letters on social media” to show a united front.

The succession dispute has raised concerns that the Taliban could splinter, complicating any peace efforts, or that powerful field commanders could defect to the Islamic State group, which has a small but growing presence in Afghanistan.

Around 50 Taliban fighters in the northern Kunduz province joined the IS group three days ago after being offered money, the provincial governor’s spokesman, Abdul Wadood Wahidi, said. The move set off fierce clashes in which the Taliban arrested the defectors, he said.

The Afghan government has banned any public mourning for Mullah Omar, saying late Monday that it would cause “anguish and humiliation” for those who have lost loved ones in the war with the Taliban. A statement from the National Directorate of Security said public gatherings to commemorate his death would be a “legitimate military target.”