Turkish President Erdogan says US offering Patriot systems if S-400s remain unboxed

The United States has offered to sell Turkey its Patriot missile defence system if Ankara promises not to operate rival Russian S-400 systems, Turkish President Tayyip Erdogan said.

Two Turkish officials reportedly said that Turkey was evaluating the US offer but that Ankara had not changed its plans for the Russian S-400 systems, which it has said it will start to activate next month.

NATO allies Turkey and the United States have been at loggerheads over Ankara's decision to buy Russia's S-400s missiles, which Washington says are incompatible with the alliance's defence systems.

Speaking to reporters on his return flight from Brussels, Erdogan said Ankara had told Washington to deploy Patriot systems to Turkey and that it was ready to purchase the systems from the United States as well.

"We made this offer to the United States on the Patriot: If you are going to give us Patriots, then do it. We can also buy Patriots from you," he said.

"They also softened significantly on this S-400 issue. They are now at the point of 'promise us you won't make the S-400s operational'," Erdogan added.

Previous talks between Turkey and the United States on the matter collapsed over a host of issues, from the S-400s to Ankara's dissatisfaction with Washington's terms. 

Turkey has said it will only agree to an offer if it includes technology transfer and joint production terms.

While ties between Ankara and Washington have been strained, the United States has offered support for its ally as it battle to stop Russia-backed Syrian government advances in Idlib, news agency Reuters reported.

But US officials said on Tuesday Ankara had to clarify its position on the S-400s for their security ties to advance, the report added.