MOSCOW: A Syrian plane detained by Turkey en route from Moscow to Damascus because of suspicions it was carrying military equipment was carrying no Russian weapons, a source in a Russian arms exporting agency told Interfax on Thursday.

"Neither weapons nor any kind of systems or parts for military equipment were on board or could have been on board," the news agency quoted the source as saying on condition of anonymity.

Military jets escorted the Damascus-bound Airbus A-320, carrying about 30 passengers from Moscow, into Ankara airport late on Wednesday after Turkey received intelligence that it was carrying military supplies.

Parts of the cargo were seized in Turkey before the passenger jet continued its trip. No details were given of its contents.

Russia has been one of Syrian President Bashar al-Assad's biggest allies, blocking three U.N. Security Council resolutions meant to pile pressure on him while selling his armed forces nearly $1 billion in arms last year.

The arms source said Moscow has not stopped its arms exports to Damascus, despite mixed signals from Russia over whether it has continued to supply Syria with weapons since the worsening of violence between rebels and forces loyal to Assad.

"If we needed to send any kind of military-technical equipment or arms it would have been carried out properly and not through any illegal means, certainly not on a civilian aircraft," the source said.

President Vladimir Putin said in June that Russia does not send Syria weapons that could be used in a civil conflict.

Russia demanded an explanation from Turkish authorities for the interception of the plane which took off from Moscow's Vnukovo Airport on Wednesday, Interfax cited a Russia Foreign Ministry source as saying on Thursday.