The United States and NATO said on Wednesday, January 27 that they delivered written replies to security demands that Russia had made, Deutsche Welle reports.

It comes amid heightened tensions and repeated warnings that Russia could be preparing military action against Ukraine.

Russia had demanded security guarantees that Ukraine would never join NATO, and that the alliance stops its eastward expansion — which the U.S. and NATO rejected.

US Secretary of State Antony Blinken said the document addressed Moscow's concerns and raised those of Washington's allies but made no concessions.

"Putting things in writing is... a good way to make sure we're as precise as possible, and the Russians understand our positions, our ideas, as clearly as possible. Right now, the document is with them and the ball is in their court," he told reporters.

Blinken said he would speak with his Russian counterpart, Sergey Lavrov, in the coming days.

The letter would not be made public, "because we think that diplomacy has the best chance to succeed," Blinken said.