MOSCOW (Reuters) - Russia plans to improve and expand its naval and air bases in Syria, Interfax news agency reported on Sunday, citing an unnamed source, as Moscow cements its presence in the Middle Eastern country, its only overseas military deployment.

The source told Interfax that Russia will start repairing a second runway at Hmeimin air base near Latakia, while the Tartus naval base will be upgraded in order to handle bigger ships such as cruisers.

President Vladimir Putin has announced a partial withdrawal of Russian forces from Syria, where they have been helping forces loyal to President Bashar al-Assad. But Moscow wants to retain a permanent presence both in Hmeimin and Tartus.

The source also told Interfax that Russia will still deploy S-300 surface-to-air defense systems and Bastion coastal missile launchers in Tartus.