Berlin - Syrian President Bashar al-Assad is having second thoughts about helping Iran with its controversial nuclear programme, German news magazine Der Spiegel reported Saturday, quoting unspecified intelligence reports.

The weekly said North Korea had also provided assistance to Iran at a Syrian facility bombed by Israeli warplanes in September 2007.

Experts believe the site at al-Kibar was used to produce nuclear material the Iranian regime needed to make a bomb, the magazine reported.

North Korean scientists worked alongside Syrians and Iranians at the site, where a reactor was being built to produce weapons-grade plutonium, Der Spiegel quoted the intelligence reports as saying.

The report said Iranian scientists had made progress in enriching uranium but had no experience with plutonium and sought the help of the North Koreans.

Inspectors from the International Atomic Energy Agency, the United Nations nuclear watchdog, are due to travel to Syria on Sunday to investigate whether the country was building an undeclared reactor.

Syria maintains the site, which satellite images show has since been razed, was a military installation and not a nuclear facility.

Iran says its nuclear programme is not geared towards making weapons but to generating electricity for its growing population. Tehran's decision to begin enriching uranium in 2006 triggered Western sanctions.

Der Spiegel, which did not elaborate on al-Assad's reported change of heart, also said Iran, Syria and North Korea had apparently been cooperating in the production of chemical weapons.

It cited an explosion near the Syrian city of Aleppo in July 2007, during which many were reported to have died when quantities of mustard gas and the nerve agent Sarin escaped.

In addition to 15 Syrian military officials, dozens of Iranian "rocket scientists" and three North Koreans were among those killed, the magazine said. (dpa)