Qatar is finalising a deal to buy Russian S-400 air defence systems, the isolated Gulf state's ambassador to Moscow said on Thursday.

“Negotiations in this direction are in an advanced stage,” Fahad bin Mohammed Al-Attiyah told Russia's TASS state news agency. Talks were also ongoing for the purchase of “ground force technologies,” he added.

The announcement came after the historic visit of Saudi Arabia's King Salman to Moscow last year, when Riyadh signed preliminary agreements to buy S-400 air defence systems and anti-tank guided missile systems.

Led by Saudi Arabia, the United Arab Emirates, Bahrain and Egypt cut ties with Qatar last June over Doha's alleged ties to extremists and Iran. Qatar denies the charges.

It has stepped up diplomatic and trade efforts elsewhere in a bid to counter its regional isolation.

Last month, Russia announced it had completed negotiations with Turkey for the sale of an S-400 air defence missile system, raising eyebrows among Turkey's NATO partners.