Kabul, Jun 16 (IANS): The Islamic State group captured part of Afghanistan's Tora Bora mountainous region, known for having been Osama Bin Laden's hiding place after the 9/11 attacks, said a regional government spokesman.

Attaullah Khogyanai, spokesman for the governor of the eastern Nangarhar province where Tora Bora is located, confirmed to Efe that the region had been captured, spelling the first huge victory for the IS in Afghanistan in two months.

However, he stressed that security forces had already launched an offensive to get rid of the IS.

"Our forces have been engaged in operations in Pachir-Agam district, and they are now close to Tora Bora," Khogyanai told Efe.

The Taliban, which controlled this region close to the Pakistani border, admitted that the IS took control of the "mountainous part" of the area.

Taliban spokesman Zabihullah Mujahid said that the IS fighters gradually came to gain control of the area in the last three days, following nearly week-long clashes between the two groups.

"Our Mujahideen yesterday (Wednesday) attacked to push them (the IS) back, but the Americans bombed our Mujahideen and for now our operation has been halted in the area," he said.

He emphasised that most parts of Tora-Bora were still under the Taliban control, and added that they had sent reinforcements to carry out a fresh counterattack.

This is the most significant IS triumph since April 13 when it lost its main base during a US bombing in Achin district of Nangarhar province.

The US had then dropped the powerful GBU-43 Massive Ordnance Air Blast device, dubbed the "mother of all bombs", to wipe out a cave and bunker complex, killing around a hundred IS fighters and commanders.

The tunnels of Tora Bora were built by the Taliban with the US help during the Soviet-Afghan war (1979-89), and later served as an Al Qaeda and the Taliban stronghold during the 2001 US invasion.