Afghan authorities have discovered mass graves containing the bodies of ex-President Mohammad Daud Khan, family members and aides, who were killed in a Soviet-backed coup three decades ago, his grandson said.

"Two mass graves, one containing 16 bodies and the other 12, were found. We recognised by their shoes and clothes that the graves belonged to the deceased Daud Khan, his family and cabinet members," his grandson Mahmoud Ghazi Daud told reporters on Saturday.

He did not give further details on the identification process or provide more details on the discovery.

The graves were recently discovered by a commission appointed in April by President Hamid Karzai at the request of Daud Khan's family.

Daud Khan, Afghanistan's first president, was shot dead in the presidential palace in a military coup in April 1978.

Many Afghans see it as one of their country's darkest days, because it was followed by a decade of Soviet occupation, civil war, and the rise of the Taliban, who were toppled by U.S.-led troops in 2001.

Some two million people are believed to have been killed since the 1978 coup and more than six million have fled the country.

Daud Khan came to power in a coup himself when he overthrew his cousin Zahir Shah, the last king of Afghanistan, in 1973.

He tried to counter the influence of Islamists and established a republic, introducing reforms and eventually favoured relations with the West over the Soviet Union.