Following a meeting on Monday with Russian President Vladimir Putin, who hinted some progress had been achieved in the discussions, French President Emmanuel Macron said the following days will be key in the Ukraine conflict.

Putin claimed the first meeting he had with a Western leader since the Kremlin began massing troops near its border was productive, but he also reiterated his threat of war if Ukraine joins NATO.

Russia demands security assurances, including no missile installations near its borders and a reduction in NATO's military infrastructure, as it vies for dominance in post-Cold War Europe.

Some of Russia's requests have been labeled "non-starters" by the West, but it is eager to discuss weapons control and confidence-building measures.

Macron, who has emphasized his diplomatic credentials in the run-up to probable re-election in two months, met with Russian President Vladimir Putin for more than five hours over dinner on Monday.

"The next few days will be critical," Macron said after the lunch, which featured reindeer, sweet potatoes, and blackberries.

Some of Macron's suggestions, according to Putin, might help ease the tension.

"A number of his ideas, proposals, which are probably still too early to talk about, I think it is quite possible to make the basis of our further joint steps," he said.

After Macron's meeting with Ukraine's leadership on Tuesday, the two are expected to speak again.

In 2014, Russia acquired Crimea from Ukraine, is supporting rebels in the country's east, and has amassed more than 100,000 troops along the Ukrainian border.

It has stated that it does not intend to invade, but that if its security demands are not met, it may take unspecified military action.

Since the conclusion of the Cold War three decades ago, NATO has added 14 new east European members, which Moscow perceives as an incursion on its sphere of influence and a danger to its security.