Romanian President Klaus Iohannis on Thursday welcomed French counterpart Emmanuel Macron's announcement of a possible troop deployment on NATO's Eastern flank as fears rise of a Russian attack on Ukraine.

Macron on Wednesday expressed France's "readiness to go further, and within the framework of NATO to commit to new missions ... in particular in Romania".

"I warmly welcome President Emmanuel Macron's announcement on France's readiness to participate in NATO's forward military presence in Romania," Iohannis tweeted.

"The Romania-France strategic partnership will thus be reinforced on the Eastern flank, in the Black Sea region", he added.

Across Europe fears are mounting that a major conflict could break out as Russia has tens of thousands of troops massed on the Ukrainian border.

Moscow insists it has no plans to invade but has at the same time laid down a series of demands -- including a ban on Ukraine joining NATO -- in exchange for de-escalation.

Romania, a NATO member since 2004 and which already hosts around 1,000 US troops on its territory, also said it was ready to welcome more American soldiers.

US President Joe Biden said on Wednesday that Washington would "actually increase troop presence in Poland, in Romania, et cetera, if in fact he (the Russian president) moves because we have a sacred obligation in Article 5 to defend those countries.  They are part of NATO".

"I welcome the explicit announcement of President Joe Biden to increase the US military presence in Romania, on the eastern flank, if the security situation deteriorates further", Iohannis said.