Under tight security, Frans van Anraat, 62, a Dutch businessman who is alleged to have helped Saddam Hussein to gas the Kurds of Halabja in 1988, appeared for a pre-trial hearing in Rotterdam, facing charges of complicity in genocide and international war crimes.

His request to be released until the full trial opens in November was rejected by the court.

Mr Van Anraat, who was arrested at his Amsterdam home last December, has yet to enter a plea to any of the charges.

Fred Teeven, the prosecutor, told the hearing that Mr Van Anraat was fully aware that the chemicals he was supplying were being used for chemical weapons, adducing American, UN and Iraqi information to back up the allegation, as well as correspondence to and from Mr Van Anraat.

"Van Anraat was conscious of ... the fact that his materials were going to be used for poison gas attacks," he said. "The damage and grief caused will not be rapidly, if ever, forgotten. What's more, the dossier contains very strong indications that the suspect calmly continued with the deliveries of ingredients after the gas attack on Halabja on March 16 1988."

The defence said that Mr Van Anraat did not know what Iraq intended to do with the materials he provided, and that he stopped shipments to Iraq after the Halabja attack.

There was no convincing evidence linking the material he had supplied to chemical weapons used by Iraq.

The businessman was first detained in Milan in 1989 after a request from the US, but was released two months later.

He surfaced in Baghdad, which he made his home for 14 years under a new identity: Faris Mansoor Rashid al-Bazas. After the American-led invasion of Iraq, the portly bespectacled trader moved again in April 2003.

He took a taxi to the Syrian border, then made his way to the Netherlands, where he moved into a small terrace house overlooking a canal in the west of Amsterdam.

Late last year he was about to leave the city when, alerted by telephone intercepts indicating his travel plans, the Dutch police arrested him.

Dubbed "Holland's Chemical Ali" by the Dutch media, Mr Van Anraat is the first Dutchman to be charged with international war crimes.

The Van Anraat saga goes back 20 years. The US customs service says he has been on its 10 list of most wanted suspects internationally for years.

Although the case focuses on dozens of allegedly illegal shipments of chemical precursors to Iraq via the US, Europe, Japan, and the far east, it also appears to entail cloak-and-dagger elements and intelligence cover-ups, aspects which are certain to feature in Mr Van Anraat's defence, and which could prove embarrassing to the Dutch government.

The main allegations are that between 1984 and 1989 he supplied the Saddam regime with thousands of tonnes of chemical precursors for mustard gas and nerve gas.

These gases Saddam then used against Iranians in the Iran-Iraq war and, most infamously, in "Operation Anfal" in Iraqi Kurdistan between February and September 1988, gassing, killing and maiming tens of thousands of civilians, including the 5,000 massacred in Halabja in March that year.

Mr Van Anraat has never denied supplying the chemicals. But he denies knowing that they were intended for weapons purposes, and says he was sickened by television footage of the massacre.

"The images of the gas attack on the Kurdish city Halabja were a shock," he said in a 2003 interview with a Dutch magazine, Nieuwe Revu.

"But I did not give the order to do that. How many products, such as bullets do we make in the Netherlands?"

Arnold Karskens, a prominent Dutch journalist who has been tracking Mr Van Anraat since 1991, said: "He told me it all had nothing to do with the military industry."

Wim De Bruin, an official in the Dutch prosecutor's offices, said: "We have a list of 34 shipments of precursors. Not all of them were investigated by the Americans."

There is also a string of unanswered questions about the conduct of the Dutch authorities. The Americans dropped their arrest warrant for Mr Van Anraat in 2000.

"They didn't explain why," Mr De Bruin said.

Fleeing Iraq when the Americans invaded, but without a valid Dutch passport after 14 years in the Iraqi capital, Mr Van Anraat was given a "laisser passer", a travel document enabling him to get home. "The Dutch government helped him to get back here and then refused to look into his case," said Krista van Velzen, a Socialist MP who has been regularly tabling parliamentary questions on the case.

It was then disclosed that, despite having been under investigation since December 2003, Mr Van Anraat was given a new passport last October, and that the house in Amsterdam in which he was living was, in fact, an interior ministry safe house.

There are claims that he had collaborated with Dutch intelligence for years on Iraq's weapons programmes, and that, in return, he was promised immunity and a safe haven in the Netherlands.