The Taliban have executed the brother of Amrullah Saleh, the former Afghan vice president who became one of the leaders of anti-Taliban opposition forces in the Panjshir valley, his nephew said on Friday.

The news that Saleh's brother Rohullah Azizi was killed came days after Taliban forces took control of the provincial centre of Panjshir, the last province holding out against them.

"They executed my uncle," Ebadullah Saleh told Reuters in a text message. "They killed him yesterday and would not let us bury him. They kept saying his body should rot."

The Urdu language account of the Taliban information service Alemarah said that "according to reports" Rohullah Saleh was killed during fighting in Panjshir.

Saleh, a former head of the National Directorate of Security, the intelligence service of the Western-backed government that collapsed last month, is at large though his exact location remains unclear.

The National Resistance Front of Afghanistan, which groups opposition forces loyal to local leader Ahmad Massoud, has pledged to continue opposing the Taliban even after the fall of Panjshir's provincial capital Bazarak.