KABUL - Islamic State on Monday released an audio tape it said was of the movement's leader for Afghanistan, raising doubts over whether he was killed in a US drone strike on Friday.

According to Afghan intelligence agency, Hafez Saeed was killed late on Friday in the Achin district of Nangarhar province late on Friday. Achin fell to fighters loyal to Saeed last month after heavy clashes with Taliban militants. A former Taliban commander, Saeed switched allegiance to the Middle East based movement last year, raising the Islamic State's black banner and declaring a "province of Khorasan", covering Afghanistan and Pakistan.

The audio recording posted on Islamic State's Arabic website could not be independently verified and it was unclear from the content when it was recorded.

Islamic State figures have been targets for US drone strikes, which killed three other IS commanders in the same area in a week, including Shahidullah Shahid and Gul Zaman. "We are ready to sacrifice our villages and homes," he said. He also referenced battles between Taliban fighters and the new IS offshoots in Nangarhar. "We are defending ourselves," he said.

After pushing out the Taliban insurgents, Islamic State fighters have in the past two months gained ground in several districts of Nangarhar province.

Meanwhile, an influential Afghan militant faction on Monday denied reports that it had shifted loyalty to Islamic State's budding movement in the region.

A spokesman for Hizb-i-Islami, led by Afghan commander Gulbuddin Hekmatyar, said a statement that had circulated in Afghan media last week alleging Hekmatyar had thrown his support behind the ultra-hardline militant movement also known as ISIS was a fake. "It was not true. None of us had issued any such statement in support of ISIS in Afghanistan against the Afghan Taliban," spokesman Haroon Zarghoon said.

Any shift by Hekmatyar, believed to command the loyalty of fighters in Afghanistan's eastern Kunar and Nuristan provinces, would boost Islamic State's expansionist ambitions in Afghanistan and Pakistan as a rival to the main Taliban insurgency.

US drone strikes last week killed several leaders of the new IS offshoots, who are mostly former Taliban, in the eastern province of Nangarhar.

Afghan intelligence said the movement's chief for Afghanistan and Pakistan, Hafez Saeed, was killed on Friday, although an IS website cast doubt on this by releasing an undated audio message purportedly from him on Monday.

Hekmatyar became a hero to many Afghans while leading mujahideen fighters against the Soviet occupation of the country in the 1980s. In the civil war of the early 1990s, forces led by him took part in fighting in Kabul that is estimated to have killed tens of thousands of people.

A former Afghan prime minister, he was designated a global terrorist by the US State Department in 2003 for his links to al Qaeda and the Taliban. More recently, he is believed to have developed a rivalry with the Taliban's supreme leader Mullah Mohammad Omar.

Hekmatyar left Afghanistan in the mid-1990s and is believed to be in Pakistan, although his exact location is unknown. Many of his former supporters have joined either the Afghan government or the Taliban.