ISLAMABAD — Abdul Qadeer Khan, a controversial figure known as the father of Pakistan's nuclear bomb, died Sunday of COVID-19 following a lengthy illness, his family said. He was 85. 

Khan, who launched Pakistan on the path to becoming a nuclear weapons power in the early 1970s, died in a hospital in the capital Islamabad, Interior Minister Sheikh Rasheed Ahmad said. 

Thousands of people attended a state funeral at the massive white-marble Faisal Mosque in the capital. His body was carried by an honor guard and military and political dignitaries offered funeral prayers. 

Flags in Pakistan flew at half-staff.

Khan was mired in controversy that began even before he returned to Pakistan from the Netherlands in the 1970s, where he had worked at a nuclear research facility. 

He was later accused of stealing the centrifuge uranium enrichment technology from the Netherlands facility that he would later use to develop Pakistan's first nuclear weapon, according to research done by the Carnegie Endowment for International Peace.

Khan, who held a doctorate in metallurgical engineering from the Catholic University of Leuven in Belgium, offered to launch Pakistan's nuclear weapons program in 1974 after neighbor India conducted its first "peaceful nuclear explosion."

He reached out to then-Prime Minister Zulfikar Ali Bhutto offering technology for Pakistan's own nuclear weapons program. Still smarting from the 1971 loss of East Pakistan, which became Bangladesh, as well as the capture of 90,000 Pakistani soldiers by India, Bhutto embraced the offer. He famously said: "We (Pakistanis) will eat grass, even go hungry, but we will have our own (nuclear bomb)."

Since then, Pakistan has relentlessly pursued its nuclear weapons program in tandem with India. Both are declared nuclear weapons states after they conducted tit-for-tat nuclear weapons tests in 1998.

Pakistan's nuclear program and Khan's involvement have long been the subject of allegations and criticism.

Khan was accused by the U.S. of trading nuclear secrets to neighbor Iran and to North Korea in the 1990s after Washington sanctioned Pakistan for its nuclear weapons program. For 10 years during the Soviet occupation of neighboring Afghanistan, successive U.S. presidents certified Pakistan was not developing nuclear weapons. The certification was necessary under American law to allow U.S. aid to anti-communist Afghan rebels through Pakistan. 

But in 1990, just months after the 1989 withdrawal of Soviet troops from Afghanistan, Washington slapped Pakistan with crippling sanctions ending all aid to the country, including military and humanitarian. 

Pakistan was accused of selling nuclear weapons technology to North Korea in exchange for its No-Dong missiles capable of carrying nuclear warheads. A 2003 Congressional Research Report said that while it was difficult to pinpoint the genesis of Pakistan's nuclear cooperation with North Korea, it likely began in the mid-1990s

At home in Pakistan, Khan was heralded as a hero and the father of the nuclear bomb. Radical religious parties called him the father of the only Islamic nuclear bomb.

Khan was rejected by Pakistan's dictator President Gen. Pervez Musharraf after 2001, when details of Khan's alleged sales of nuclear secrets came under renewed scrutiny. Khan bitterly denounced Musharraf and his attempt to distance the state from his activities, always denying he engaged in any secret selling or clandestine nuclear weapons technology exchanges.

In recent years, Khan mostly lived out of the public eye and tributes from fellow scientists and Pakistani politicians began soon after his death.

Prime Minister Imran Khan called him a "national icon," whose nuclear weapons program "provided us security against an aggressive much larger nuclear neighbor. For the people of Pakistan he was a national icon."

Fellow scientist Dr. Samar Mubarakmand said Khan was a national treasure who defied Western attempts to stifle Pakistan's nuclear program.

"It was unthinkable for the west that Pakistan would make any breakthrough but finally they had to acknowledge Dr. Khan's achievement of making the country's nuclear weapons," he said.

Khan passed at the KRL Hospital in in Islamabad.