SADDAM HUSSEIN has ordered his scientists to resume work on a programme aimed at making a nuclear bomb, a defector warned yesterday.

The Iraqi dictator, whose efforts to make atomic weapons were thwarted by United Nations inspectors after the Gulf war in 1991, revived the plans two years ago, the defector said.

Scientists who had previously worked on the weapons programme were made to return to their duties in August 1998, four months before Saddam expelled the inspectors.

According to Salman Yassin Zweir, a design engineer who was employed by the Iraqi Atomic Energy Commission for 13 years, the instruction came in a document marked "top secret" which identified a research centre on Al-Jadriya Street, Baghdad, as the headqarters of the new operation.

Zweir was arrested and tortured after refusing to go back to the programme. He escaped to Jordan, where he spoke for the first time last week after being reunited with his wife, who was also tortured, and their two sons, aged seven and six.

"Saddam is very proud of his nuclear team," said Zweir, 39. "He will never give up the dream of being the first Arab leader to have a nuclear bomb."

American intelligence officials will now debrief Zweir, whose information will raise international concern that Saddam is intent on developing weapons of mass destruction.

Colin Powell, the retired Gulf war general named by President-elect George W Bush as the next secretary of state, is expected to use the threat to press the case in Europe for America's so-called "son of star wars" national missile defence system.

A senior western diplomat said last night: "This is the first concrete evidence of what we feared might be happening."

Zweir will also be interviewed by officials from the International Atomic Energy Agency (IAEA) in Vienna, which carried out more than 1,000 inspections between 1991 and 1997 to satisfy the UN security council that everything possible had been done to dismantle Iraq's nuclear weapons programme.

"We will investigate the evidence," said Hans Meyer, a spokesman.

Zweir graduated from Baghdad University and joined the atomic energy commission in 1985 as a mechanical engineer on a salary of $1,000 a month, double the money earned by an average government official with 15 years' experience.

He signed an agreement that made it clear he would be executed if ever he left his job or revealed Iraq's nuclear secrets. "As of today, I have broken both conditions," he said.

As a member of Iraq's scientific elite, Zweir had a comfortable government villa in the Khairallah Tulfah complex in Baghdad. Security agents drove him to work and back daily, and he assumed that both his house and his car were bugged.

Zweir worked on two methods of producing highly enriched uranium for a nuclear weapon. According to UN inspectors, the commission was between one and four years away from making a bomb when its main facilities were destroyed in the Gulf war.

Based at a complex named al-Krayat on the Tigris River on the outskirts of Baghdad, Zweir helped design gas centrifuges that yielded small amounts of highly enriched uranium, although not enough for a bomb.

For part of the time, Zweir worked under Dr Jaafar Jaafar, the head of the atomic commission. The weapons programme, known as Project 3000, was supervised by Hussein Kamel, Saddam's son-in-law, who was later executed.

Kamel put the team under enormous pressure, Zweir said. "He would say, 'You must complete this work in three months.' There was no life outside work."

After the Gulf war halted the programme, Iraq at first denied that it had existed. In a little-noticed speech last September, however, Saddam said his nuclear scientists were part of the fight against Iraq's enemies.

Zweir said the Iraqi security service had moved technical components around during and after the war to conceal them from allied bombers and, later, from UN inspectors. "Only section heads could speak to the inspectors," he said. "They lied and lied and lied."

The first Zweir knew of the resumption of the weapons programme was an order to leave his work on civilian projects, including a suspension bridge in Baghdad, and report to the atomic commisson's engineering design unit. The order was signed by Mehdi Shuqr Ghali, the programme's director.

"I felt I was being asked to participate in a filthy act," he said. "I could not do it."

Within hours of his refusal to rejoin, he was arrested in his office and taken to a military intelligence prison at al-Kadamiya. He was punched, kicked and beaten with iron bars for three weeks.

After losing consciousness, he was taken to hospital, apparently because his jailers did not want him to die. Following the intervention of a hospital employee who knew his family, he was smuggled to a farm in southern Iraq and fled to Jordan in October 1998.

Charles Duelfer, the former deputy head of UN inspectors in Iraq, said last night he was "very concerned" to hear Zweir's story. "When we were working in Iraq there was a pattern that appeared to show ongoing research, but we never found direct evidence," he said.

Powell indicated last week that he would resist growing international pressure to lift UN sanctions against Iraq until Saddam accounted fully for all weapons of mass destruction.