Damascus and Pyongyang helped Iran to develop its nuclear programme through the construction of a suspected nuclear site in Syria that Israel destroyed last September, Der Spiegel reported.

But the Syrian president Bashar al-Assad is considering withdrawing his support for the Iranian programme, added the German newsweekly in its next edition out Monday, quoting German secret service reports.

According to those intelligence reports, it said, a joint plan by Syria, North Korea and Iran for a nuclear reactor for military use was to have been developed at the Al-Kibar site in the east of Syria.

The site -- to be inspected next week by the International Atomic Energy Agency (IAEA) -- was destroyed by Israeli warplanes with Washington's support. Syria denied it has military purposes.

The reports cited by Der Speigel claimed that North Korea was to help Iranian scientists to advance their nuclear programme, and that Al-Kibar was to have been used as a temporary site for Iran to develop a nuclear bomb until it was able to do so on its own territory.

The plan was discussed during a visit by Iranian President Mamhoud Ahmadinejad to Syria in 2006, according to the magazine.

The three countries also cooperated in the production of chemical weapons, said Der Speigel, quoting the same source. At the time of an explosion at a chemical site in July 2007, 15 Syrian soldiers, 12 Iranian engineers and three North Koreans were among the victims.

Ten months after the destruction of the Al-Kibar site, on the basis of allegations that a nuclear reactor was being built there with the aid of North Korea, the IAEA said it was sending experts to Syria to investigate.

Documents and detailed photographs supplied in April by Washington to the IAEA backed up the suspicions, but Syria rejected the allegations describing them as "ridiculous."

Iran and Syria, both parties to the nuclear non-proliferation treaty, signed a memorandum of cooperation at the end of May on the two countries' "independence and territorial integrity."

The alliance between the two neighbours, which goes back to the 1979 Iranian revolution, was strengthened in 2006 with the signing of an agreement on military cooperation.