Officers posing as would-be buyers have found 20 kilograms of the drug hidden in a car, the latest in a string of increasingly large seizures in the past year.

The Afghan-produced heroin comes in via Iraq's porous border with Iran, creating what United Nations officials say is an important new drug route to Europe.

During Saddam Hussein's rule, heroin was virtually unknown in Iraq because of his police-state law enforcement, which imposed the death penalty even for possession.

Since his fall the lawless environment has offered the perfect conditions for smuggling, promising a lucrative income for terrorists and criminals.

Some Iraqis can now add drug addiction to their existing woes of car bombs, kidnappings and a lack of jobs.

The 20-kilogram seizure took place in the Shiite holy city of Kerbala, 160 kilometres south of Baghdad, where the regular Shiite pilgrimages from Iran give smugglers easy cover.

"We arrested three Iraqis with 20 kilograms of heroin and 40 kilograms of hashish. Half of the drugs were hidden inside the car's body in a professional manner," said Major Mehdi Saleh, head of Kerbala's main crimes unit.

"This is our biggest seizure but it's not the first. We have carried out at least 30 operations like this in the past year."

The seizure followed warnings from UN officials in May that Afghan traffickers were allying with insurgents to turn Iraq into a leading drugs transit area between Asia and Europe.

"Whether it is due to war or disaster, weakening of border controls and security infrastructure make countries into convenient logistic and transit points, not only for international terrorists and militants but also for drug traffickers," said Hamid Ghodse, the president of the International Narcotics Control Board.

Iraq's new government is training its fledgling police force in drug-fighting measures, but says drugs will be given little priority as long as the fight against insurgents continues.

Raad Mehdi Abdul Saad, of the Interior Ministry's new drugs office, said: "It happens because we have a weak security system and the border is not protected by the Iraqi forces. For the past year I have been asking for sniffer dogs at the borders but there is no response."

Heroin is increasingly popular among Iraqis, and figures compiled by Iraq's Health Ministry last year estimated that Kerbala alone had almost 1000 addicts. British-controlled Amara, a smaller city of 300,000 near the Iranian border, had 500.

"We don't have updated figures yet, but we would say that in the past year those figures have probably doubled," said Sarwan Kamel Ali, the head of the Health Ministry's new anti-drugs program.

Addiction is worst among Iraq's Shiites, who tend to be poor and whose religious faith strictly forbids other stimulants such as alcohol.

-- Saddam's chief lawyer has dismissed as "invalid" statements from the Iraqi Government that the former president's trial will begin on October 19, and says he needs "years" just to read the 36 tonnes of filed evidence.

"The defence team has not been informed about the decision and has not signed it. It is invalid," Khalil Dulaimi said, adding that he did not recognise the legitimacy of the special tribunal set up to try Saddam and his aides.