President Joe Biden warned Russian President Vladimir Putin on Tuesday that the West would impose “strong economic” sanctions and “other measures” on Russia if it invades Ukraine, while Putin demanded guarantees that NATO would not expand farther eastward.

The two leaders held two hours of virtual talks on Ukraine and other disputes in a video call about U.S.-Russian relations, as Russia masses tens of thousands of troops on Ukraine’s border, Reuters reported.

Putin responded to the warning with a demand for reliable, legally binding guarantees against NATO expansion eastward and complained about NATO attempts to “develop” Ukrainian territory,” the Kremlin said.

The White House said Biden did not make any guarantees to limit NATO expansion with regard to Ukraine.

“I will tell you clearly and directly he made no such commitments or concessions. He stands by the proposition that countries should be able to freely choose who they associate with,” Biden’s national security adviser Jake Sullivan told reporters.

No breakthroughs were reported but both sides agreed to continue communications, a development that could lower global tensions.

The Kremlin has denied harboring any intention to attack Ukraine and has said a troop buildup on its southern border is defensive, but neighboring nations are sounding alarms, Reuters reported.