Former King of Afghanistan Mohammad Zahir Shah has died after battling a long illness.

Zahir Shah, whose 40-year reign until his exile in 1973 coincided with one of the most peaceful periods in Afghanistan's recent history, passed away this morning aged 92.

State television interrupted its normal broadcast and a woman dressed black with a black headscarf announced Zahir Shah had died. Prayers and recitals from the Koran followed.

President Hamid Karzai said: "With paramount grief, I would like to inform my countrymen that ... Mohammad Zahir Shah has bid farewell to this mortal world."

Describing him as the founder of Afghanistan's democracy and a symbol of national unity, Karzai announced three days of national mourning for the former king and ordered flags to be flown at half mast.

Zahir Shah ruled Afghanistan from 1933 until he was deposed by his cousin in 1973. He lived in exile in Italy before returning home as an ordinary citizen in 2002, but was accorded the honorary title "father of the nation".

Zahir Shah came from a long line of ethnic Pashtun rulers and is a distant relative of President Karzai.

The former king's reign is remembered as one of the most tranquil periods of Afghanistan's turbulent history.

Born in Kabul on October 15, 1914, Zahir Shah received part of his education in France and returned to Kabul for military training.

He ascended the throne in 1933 after his father was assassinated by a deranged student.

For two decades, the bookish king remained in the shadows, allowing three uncles to run the government.

But he gradually gained in confidence and took full control in 1953, overseeing a cautious modernisation of his backward realm.

In 1973, while holidaying in Italy, Zahir Shah was ousted in a bloodless coup orchestrated by his cousin and brother-in-law, Prince Daoud, ending two centuries of rule by the Durrani dynasty.