President Vladimir Putin offered Russian assistance on Monday to Syria and Turkey after a major earthquake of magnitude 7.8 killed more than 500 people and injured thousands in the two countries.

Russia has strong relations with both Syria and Turkey: Putin backed President Bashar al-Assad in the civil war and has a strong rapport with President Tayyip Erdogan of Turkey, a NATO member which has sought to mediate in the Ukraine war.

"Please accept my deep condolences on the numerous human casualties and large-scale destruction caused by a powerful earthquake in your country,” Putin said in his message to Erdogan.

"We are ready to provide the necessary assistance in this regard.”

In a similar message to Assad, Putin said Russia shared ”the sadness and pain of those who lost their loved ones” and said Russia was ready to provide help.

Russia said it had two Ilyushin-76 aircraft with rescuers on board that were ready to fly to Turkey to help the rescue effort. Russia's emergency ministry said 100 rescuers had been put on alert.

Russia backed Assad in Syria's civil war, launching a military campaign that helped turn the tide of the war in his favour even though the West had called for the Syrian leader to go.

Russia has a naval base in Tartus, on the Syrian coast, and operates the Khmeimim air base north of Tartus.

Russia's defence ministry said its military facilities in Syria had not been damaged by the earthquake.

Nuclear plant

Separately, an official from Russia's state atomic energy company Rosatom said the Akkuyu nuclear power plant it is building in southern Turkey was also not damaged by the quake.

"Nevertheless, we are carrying out extensive diagnostic measures to make sure that construction and installation operations can continue safely,” the RIA news agency quoted Rosatom official Anastasia Zoteeva as saying.

Armenia, which was struck by a devastating earthquake in 1988, also expressed its sadness over Monday's earthquake, even though the former Soviet republic which borders Turkey has no diplomatic ties with Ankara due to disputes over history.

Yerevan says 1.5 million Armenians were killed in a genocide committed by the Ottoman Empire, the predecessor to modern Turkey, in 1915. Ankara contests the figures and denies the killings were systematic or constitute a genocide.

"Saddened by the news of the devastating earthquake in Turkey and Syria that resulted in the loss of so many lives,” Armenian Prime Minister Nikol Pashinyan said.

"Our deepest condolences to the families of the victims and we wish a speedy recovery to the injured. Armenia is ready to provide assistance.”