Iran on Monday "strongly" condemned the Taliban's military offensive against holdout fighters in Afghanistan's Panjshir Valley, as the Islamist group claimed it had taken control of the area.

"The news coming from Panjshir is truly worrying," Iran's foreign ministry spokesman Saeed Khatibzadeh told reporters. "The assault is strongly condemned."

Iran, the region's dominant Muslim Shiite power, had until now refrained from criticising the Taliban since the Sunni group seized Kabul on August 15.

The Taliban on Monday claimed victory in the mountainous Panjshir area, with a spokesman declaring "our country is completely taken out of the quagmire of war", three weeks after the Islamists captured the capital.

But the National Resistance Front (NRF) -- made up of anti-Taliban militia and former Afghan security forces -- said its fighters were still present in "strategic positions" across the valley, and that they were continuing the struggle.

"On the question of Panjshir, I have insisted on the fact that it be resolved by dialogue in the presence of all the Afghan elders," Khatibzadeh said.

"The Taliban must equally respect their obligations in terms of international law, and their commitments," he added, affirming that "Iran will work to put an end to all the suffering of the Afghan people in favour of establishing a representative government for all Afghans".

Alluding to Pakistan, Khatibzadeh said Iran condemned "all foreign interference" in Afghan affairs.

"We would like to inform our friends, and those who might make the strategic error of entering Afghanistan with different intentions, that Afghanistan is not a country which accepts the enemy (or) the aggressor" on its soil, Iran's foreign ministry spokesman added.

Iran, which shares a 900-kilometre border with Afghanistan, did not recognise the Taliban during their 1996 to 2001 stint in power.

Already host to nearly 3.5 million Afghans, and fearing a new influx, Tehran has however sought to sketch a rapprochement with the Taliban since their lightning seizure of Kabul amid the US withdrawal last month.