Saddam Hussein's senior weapons adviser has surrendered to US military authorities, insisting that Iraq had no weapons of mass destruction and that the US-led invasion was unjustified.

Lieutenant General Amir al-Saadi was Saddam's science adviser, and the leading Iraqi wanted for questioning about the country's chemical weapons programme. He oversaw Iraq's chemical programme, and is believed to have in-depth knowledge of other weapons programmes.

Lt-Gen al-Saadi arranged his surrender with the help of Germany's ZDF television network. The network said it was asked to film him leaving his Baghdad villa with his German wife, Helga, and presenting himself to a US warrant officer, who escorted him away.

A spokesman for US central command in Qatar told Reuters that Lt-Gen al-Saadi was in custody after surrendering, but said no other details were available.

In an interview with ZDF, the science adviser insisted that he had been honest in his dealings with weapons inspectors before the war, saying: "I was knowledgeable about these programmes. I was telling the truth, always telling the truth. I never told anything but the truth, and time will bear me out.

"You will see. There will be no difference after this war. I am saying this for posterity and for history and not to defend a regime ... I am saying exactly what I believe in, I knew. Nobody told me what to say. Never."