MOSCOW - Russia and Turkey are working on a contract for the delivery of a new batch of Russian S-400 missile systems, according to a senior official at a Russian military cooperation agency.

The latest development, reported by the Interfax news agency on Friday, comes after US President Donald Trump said at a recent NATO meeting in London that Washington was considering sanctions against Ankara over purchasing the system.

"We are looking at it now, and we're talking about it now," Trump told reporters. "As you know Turkey wanted to buy our Patriot system and the [former US President Barack] Obama administration wouldn't let them, and they only let them when they were ready to buy another system."

Amid already strained bilateral ties, Washington has suspended Ankara from the US F-35 stealth fighter jet programme, in which it was a producer and buyer, to penalise it for buying S-400 batteries this year.

Moscow hopes to seal a deal to supply Turkey with more S-400 systems in the first half of next year, the head of Russian state arms exporter Rosoboronexport said last month.

Hulusi Akar, Turkey's defence minister, has said that the purchase of the system - the first such move between a NATO member and Russia - was "not a choice but a necessity" because it was under serious threat.(FA)