ANKARA (BLOOMBERG) - United States senators warned Nato ally Turkey that it would trigger new sanctions if it goes ahead with plans to purchase additional Russian missile defence systems.

The warning comes ahead of a critical meeting between President Recep Tayyip Erdogan and Russian President Vladimir Putin in Sochi on Wednesday (Sept 29).

Turkey and Russia have been negotiating over technology transfers and local production ahead of a potential purchase of a second S-400 missile defence system.

Alexander Mikheyev, the head of Russia's state-run arms exporter Rosoboronexport, said in August that Turkey was in the final stages of negotiating the deal.

Erdogan told CBS news in an interview last week that he intends to go ahead with the purchase.

The office of Senate Foreign Relations chair Robert Menendez responded by warning that sanctions were mandated by law for "any entity that does significant business with the Russian military or intelligence sectors."

"Any new purchases by Turkey must mean new sanctions," he said on Twitter.

The US has already imposed penalties on Turkey's defence industry over the initial missile purchase, saying the Russian system could be used to gather intelligence on Lockheed Martin Corp's F-35 stealth jet.

It previously suspended Turkish defence contractors from the international program to help build the F-35.

Turkey has so far refused to jettison the first S-400 battery it acquired in 2019.