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

Such a move could further sour ties between Turkey and the United States, which has suspended Ankara from the F-35 stealth fighter jet program, in which it was a producer and buyer, to punish it for buying S-400 batteries earlier this year.

Washington has also warned of possible U.S. sanctions, saying the missiles are not compatible with NATO defenses, but has not yet imposed them. A senior U.S. State Department official said last week that Turkey needed to get rid of the S-400s it had already bought to mend fences.

But Rosoboronexport's Alexander Mikheev told RIA news agency Moscow and Ankara were actively discussing Ankara taking up an option in the original contract for it to receive more S-400 systems, with talks focused on financial questions.

"We hope that in the first half of 2020 we will sign the contract documents," RIA cited Mikheev as saying. "But I want to stress that military technical cooperation with Turkey is not limited to the supply of the S-400s. We have big plans ahead."

At a meeting in the White House earlier this month, U.S. President Donald Trump and Turkish President Tayyip Erdogan agreed to ask their respective ministers and national security advisers to work on resolving the S-400 issue.

"We need to see where we get with these efforts," broadcaster NTV reported Erdogan as saying on Tuesday of the talks, which he said would continue between the two NATO allies until April.

After the delivery of S-400 parts to Turkey began in July, Erdogan said the system would be fully deployed by April 2020.