The atomic scientist, who spent the last years of his life under heavy guard, died in the capital Islamabad, where he had recently been hospitalised with Covid-19.

Khan died after being transferred to the city's KRL Hospital with lung problems, state-run broadcaster PTV reported.

He had been admitted to the same hospital in August with Covid-19. After returning home several weeks ago, he was rushed back after his condition deteriorated.

Khan was hailed a national hero for transforming Pakistan into the world's first Islamic nuclear weapons power and strengthening its clout against rival and fellow nuclear-armed nation India.

But he was declared by the West a dangerous renegade for sharing technology with rogue nuclear states.

The news of his death sparked an outpouring of grief and praise for Khan's legacy.

"Deeply saddened by the passing of Dr A.Q. Khan," Prime Minister Imran Khan tweeted, stressing how loved the nuclear scientist had been in Pakistan due to "his critical contribution in making us a nuclear weapon state".

"For the people of Pakistan he was a national icon."

Opposition leader Shehbaz Sharif described his death as a "huge loss for the country", tweeting: "Today the nation has lost a true benefactor who served the motherland with heart and soul."

The prime minister said the scientist would be buried at Islamabad's Faisal Mosque at his request.

Interior Minister Sheikh Rashid Ahmad told journalists the scientist would be laid to rest with "full honours", with all government ministers and senior armed forces officials attending a funeral at 3:30 pm (1030 GMT) Sunday.

According to Islamic tradition, burials should take place as soon as possible, usually within 24 hours of death.

- Black market -

Khan was lauded for bringing the nation up to par with India in the atomic field and making its defences "impregnable".

But he found himself in the international crosshairs when he was accused of illegally sharing nuclear technology with Iran, Libya and North Korea.

He confessed in 2004, after the International Atomic Energy Agency -- a UN watchdog -- put Pakistani scientists at the centre of a global atomic black market.

Pardoned by the nation's military ruler Pervez Musharraf, he was instead put under house arrest for five years.

"I saved the country for the first time when I made Pakistan a nuclear nation and saved it again when I confessed and took the whole blame on myself," Khan told AFP in an interview in 2008.

After his house arrest was lifted, he was granted some freedom of movement around the leafy capital, but always flanked by authorities, who he had to inform of his every move.

On Sunday, journalists gathered behind barriers blocking off the street leading to his home in the capital as a procession of cars entered and left the property.

- Best deterrent -

Born in Bhopal, India on April 1, 1936, Khan was just a young boy when his family migrated to Pakistan during the bloody 1947 partition of the sub-continent at the end of British colonial rule.

He did a science degree at Karachi University in 1960, then went on to study metallurgical engineering in Berlin before completing advanced studies in the Netherlands and Belgium.

His crucial contribution to Pakistan's nuclear programme was the procurement of a blueprint for uranium centrifuges, which transform uranium into weapons-grade fuel for nuclear fissile material.

He was charged with stealing it from the Netherlands while working for Anglo-Dutch-German nuclear engineering consortium Urenco, and bringing it back to Pakistan in 1976.

On his return to Pakistan, then prime minister Zulfikar Ali Bhutto put Khan in charge of the government's nascent uranium enrichment project.

By 1978, his team had enriched uranium and by 1984 they were ready to detonate a nuclear device, Khan later said in a newspaper interview.

Khan maintained that nuclear defence was the best deterrent.

After Islamabad carried out atomic tests in 1998 in response to tests by India, Khan insisted Pakistan "never wanted to make nuclear weapons. It was forced to do so".

None of the controversies that dogged Khan's career appeared to dent his popularity at home.

Many schools, universities, institutes and charity hospitals across Pakistan are named after him, his portrait decorating their signs, stationery and websites.