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Israeli officials had previously denied that the plane was carrying dangerous materials.

The statement by El Al follows publication in the Dutch media of the plane's freight documents, which show that the chemical, dimethyl methylphosphonate (DMPP), which is also used in building materials, was being taken from US factory to a biological research centre outside Tel Aviv.

The Israeli authorities and the Dutch parliament have both ordered further investigations into the crash.

Local MEP Maartje Van Putten: outraged

The local MEP for the area, Maartje Van Putten said she was outraged that the plane had been allowed to fly over the city carrying such a cargo.

A spokesman for El Al said they had informed the Dutch authorities at the outset of the investigation into the crash, which killed four crew members on the plane and 39 people in the apartment complex.

"Everything was done in accordance with international regulations," he said.

The Dutch foreign ministry confirmed that it had already known about the presence of chemicals on the plane.

Survivors' complaints

Up to 300 people are believed to be suffering from the effects

Since the crash, six years ago, many residents near the site of the crash have complained of mysterious illnesses.

A report published on Wednesday by the Dutch health ministry showed that local doctors believed up to 300 residents could be suffering from effects caused by the accident.

They range from depression and nervousness to fatigue and listlessness.

Cargo was heading to Israeli plant

According to the document published in the Dutch newspaper, the chemical came from an American company in Pennsylvania and was headed for the Israel Institute for Biological Research in Ness Ziona near Tel Aviv.

Correspondents say that although the activities of the Ness Ziona institute are classified, it is believed to be a facility for the manufacturing of chemical and biological weapons and antidotes for such arms.

DMPP has other uses beyond nerve gas. It is also used in building materials as a flame retardant, and transporting sensitive chemicals by air is a well-tried practice.

BBC Europe correspondent David Eades says, however, that as a country which insists it does not manufacture weapons of mass destruction - and nerve gas is one of those - Israel is bound to come under suspicion as to the purpose of this cargo.

Israel has accused Syria, Iraq and Iran of developing chemical and biological weapons.