US Secretary of State Antony Blinken urged Russia to "immediately" de-escalate tensions and withdraw its troops from Ukraine's borders in a call Tuesday with Russian counterpart Sergei Lavrov, the State Department said.

Blinken "emphasized that further invasion of Ukraine would be met with swift and severe consequences and urged Russia to pursue a diplomatic path," the department said in a statement.

A State Department official said Blinken told Lavrov that Washington and its allies were ready to sit down and discuss the proposals both sides have set out in a series of letters to resolve the crisis.

Blinken told Lavros that the discussions "will be best advanced by de-escalation of Russia's build up military forces on Ukraine's borders."

However, the official said, "nothing we heard would give any indication that we would see a change in the coming days," in terms of de-escalation.

"We continue to hear those assurances that Russia is not planning to invade, but certainly every action we see says otherwise, with the continued buildup of troops and heavy weapons moving to the border," the official said, speaking on grounds of anonymity.

The official said that a letter sent by Lavrov to Blinken and counterparts in Europe late Monday was not Russia’s formal response to the positions the US and European allies laid out in letters to Moscow last week.

"They're still working on their formal response," that needs to be signed off on by President Vladimir Putin, the official said.

Once that response is delivered, the different sides will be able to talk about the next steps in the process, the official said.

But the US side stressed the need for Russia to draw down some of the more than 100,000 troops it has amassed on Ukraine's border, including inside Belarus.

"If President Putin does not intend war or regime change, the secretary (Blinken) told Foreign Minister Lavrov, then this is the time to pull back troops and heavy weapons and heavy weaponry," the official said.

AFP