Islamic State fighters have captured some territory around Tora Bora, the former stronghold of Osama bin Laden in Afghanistan’s eastern Nangarhar province, officials said on Wednesday.

The push and capture of the giant cave complex that once housed the late al-Qaida chief would be a major victory for the Islamic State group in its increasingly deadly rivalry with the Afghan Taliban. The caves had until now been under Taliban control.

Attahullah Khogyani, a spokesman in Nangarhar, said Isis attacks in the mountain range began late on Tuesday night. Clashes continued into the day, with Isis militants battling the Taliban and some local villagers in the area.

By Wednesday, Isis had managed to seize some territory around Tora Bora – but not the bin Laden hideout itself, Khogyani said, adding that there were unspecified casualties on both sides.

“I can confirm that the Isis fighters occupied some areas around Tora Bora, but not Tora Bora itself,” said Khogyani, referring to the cave complex from where Bin Laden and hundreds of other al-Qaida members escaped a huge US bombing campaign in December 2001.

There has been no comment from Isis or the Taliban so far.

However, Hazrat Ali, a lawmaker from Nangarhar, confirmed that at least 12 Taliban fighters had been killed in the clash. “Based on our information from local people, hundreds of Isis fighters attacked Taliban militants in Tora Bora,” said Ali.

He added that the Tora Bora mountain range, with the huge caves that once hid Bin Laden, was strategically a very important location for Isis, giving it a remote and difficult-to-access location from where to launch attacks on Afghan government forces as well as the Taliban.

Shirin Agha Faqiri, a spokesman for the army corps in eastern Nangarhar, said Isis fighters had captured much of the Tora Bora mountains, and even positioned some of their heavy artillery on the mountain peaks there.

“People and the local villagers are fleeing to other parts of the province,” he added.

Tora Bora was Bin Laden’s last hideout in Afghanistan, where he and his al-Qaida followers where hosted by the Taliban. Only a few months after the September 11 2001 terror attacks, Bin Laden escaped a US assault in Tora Bora, and later managed to flee to Pakistan.

Bin Laden was killed in a US navy Seals raid in May 2011 in the army garrison town of Abbotabad in neighboring Pakistan, a raid that many Pakistanis have felt violated their country’s sovereignty. Al-Qaida’s No 2 and Bin Laden’s deputy, Ayman al-Zawahri, took over the terror network.

The Taliban have continued their insurgency in Afghanistan and over the past two years, an affiliate of the Islamic State group, which has been fighting in Iraq and Syria, also emerged in the country, gaining a foothold in the east and clashing with the Taliban.

The US estimates that there are about 600 to 800 Isis fighters in Afghanistan, mostly in Nangarhar. The US has concentrated on fighting them while also supporting Afghan forces against the Taliban.

In April, the US used its biggest non-nuclear bomb ever dropped in combat against Isis in Nangarhar, targeting a tunnel complex carved in the mountains that Afghan forces have tried to assault repeatedly but without success.