The supreme leader of the Taliban authorities said implementing Islamic law in Afghanistan was their "lifelong responsibility" in a speech marking the third anniversary of their return to power.

The Taliban government celebrated their August 15, 2021, takeover of the capital a day early on Wednesday, in accordance with the Afghan calendar, holding military parades and gatherings across the country.

"Brothers! Our responsibility of service to religion, ruling according to sharia (Islamic law), is our lifelong responsibility," leader Hibatullah Akhundzada told security personnel at an air base in southern Kandahar on Wednesday.

The speech was posted on social media site X late Wednesday by chief government spokesman Zabihullah Mujahid.

"We will implement Allah's religion and sharia rule for ourselves and others as long as we live," said Akhundzada, in rare remarks from the reclusive leader who almost never appears in public.

"Sharia and the Islamic system are getting stronger day by day," he added.

Akhundzada rules by decree from Kandahar -- the birthplace of the Taliban movement -- and has handed down a string of orders enforcing an austere vision of Islam since the collapse of the foreign-backed government and withdrawal of US-led forces in 2021.

The Taliban government remains unrecognised by any other state, with a key sticking point being its restrictions on women, policies the United Nations has called "gender apartheid".