Russian Defense Minister Sergei Shoigu and his CAR counterpart Marie-Noelle Koyara signed the document on the sidelines of defense expo Army-2018 outside Moscow, Russian agencies reported.

The deal "will help strengthen ties in the defense sphere," Shoigu was quoted as saying after the ceremony.

There were no immediate details.

The agreement is set to deepen Moscow's involvement in the impoverished CAR, where the government is desperate to boost its armed forces in the fight against militias which control most of the country.

A UN arms embargo imposed in 2013 was last year lifted exclusively for Moscow.

It has since then sent instructors and some equipment and now provides security for President Faustin-Archange Touadera.

The deal follows the murder in late July of three Russian journalists who were ambushed in CAR while investigating a shadowy Russian mercenary group called Wagner and its possible relation to both government and rebel forces.

The investigation was funded by ex-oil tycoon Kremlin critic Mikhail Khodorkovsky.

Both CAR authorities and Moscow have labeled the killings a robbery, but Khodorkovsky's own inquiry claimed this argument "does not stand up to scrutiny".