The state-run Israeli airline, El Al, admitted on Thursday that its aircraft was carrying a chemical which is used in the production of the nerve gas sarin.

But a statement from the office of the Israeli Prime Minister Binyamin Netanyahu, quoted by Israel radio, said "the material was non-toxic and was to have been used to test filters that protect against chemical weapons".

"Israeli Government and aviation authorities acknowledged that the cargo included 190 litres of the chemical dimethyl methylphosphonate, but they insist the material was non-toxic and that it had been clearly listed on the cargo manifest in accordance with international regulations," the radio said.

Special correspondent Ben Brown: "Sarin is one of the deadliest substances concocted by man"

On Wednesday the Dutch media, citing the plane's freight documents, said the plane was carrying the chemical, which was being taken from a US factory to the Institute for Biological Research in Ness Ziona near Tel Aviv.

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

Questions raised

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

Correspondents say that the activities of the Ness Ziona institute, which was to receive the chemical, are classified.

But 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.