Iran warned Wednesday it will not tolerate "terrorists" near its border with Azerbaijan, after France and Russia raised the alarm over the deployment of Syrian militants in the Karabakh conflict.

"It is unacceptable for us that some people want to send terrorists from Syria and other places towards regions near our frontiers," President Hassan Rouhani said, quoted on state television.

Iran borders Armenian-held areas of Azerbaijan near Nagorno-Karabakh that have seen fighting.

Armenia and Azerbaijan have for decades been locked in a conflict over Nagorno-Karabakh, an ethnically Armenian area which broke away from Baku in a 1990s war that cost about 30,000 lives.

Heavy fighting erupted on September 27 in one of the most combustible frozen conflicts left over from the collapse of the Soviet Union.

Turkey has been accused of deploying fighters from Syria to support Azerbaijan in Karabakh.

French President Emmanuel Macron said Ankara had sent Syrian "jihadists" to the region, accusing Turkey of crossing a "red line".

Turkey has not responded publicly.

Russia and Armenia have also said that fighters from Syria and Libya are being deployed on the Azeri side in the conflict.

Rouhani, which has good relations with both Yerevan and Baku, reiterated Wednesday that "occupation is in no case acceptable".

"Everyone" must "accept the reality... and respect other countries' territorial integrity", he said.

Rouhani at the same time condemned "those who, on one side or the other, pour oil on the fire", without naming Turkey which has declared open support for Azeri military action to reclaim the enclave.

Iran has called on both Armenia and Azerbaijan to cease hostilities and offered to facilitate talks.

On Saturday, Tehran warned against any "intrusion" after mortar fire hit Iranian villages along the border.

Fars news agency reported last Thursday that police dispersed demonstrations in northwest Iran in support of Azerbaijan. 

The Islamic republic is home to a large Azeri community, mainly in the northwest. 

According to some estimates, Azeris make up 10 million of the 80-million population of Iran, which is also home to almost 100,000 Armenians.