US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov will meet face-to-face for the first time since the crisis escalated, after a conference in Paris attended by all five permanent members of the UN Security Council.
NATO and Russia will hold parallel talks in Brussels amid concerns that a standoff between Russian and Ukrainian soldiers in Crimea could still spark violence, or that Moscow could also intervene in Russian-speaking eastern Ukraine.
French Foreign Minister Laurent Fabius said European Union leaders meeting in Brussels on Thursday could decide on sanctions against Russia if there is no "de-escalation" by then.
President Vladimir Putin on Tuesday defended Russia's actions in Crimea, a strategic Black Sea peninsula that is part of Ukraine but used to be Russian territory, and said he would use force only as a last resort.
This eased market fears of a war over the former Soviet republic. But Russian forces remain in control of the region and Putin gave no sign of pulling servicemen, based in Crimea as part of the Black Sea Fleet, back to base.
"What he wants above all is a new empire, like the USSR but called Russia," former Ukrainian President Viktor Yushchenko told France's Europe 1 radio.
In Washington, US President Barack Obama acknowledged that Russia had legitimate interests in Ukraine but said that did not give Putin the right to intervene militarily.
"President Putin seems to have a different set of lawyers making a different set of interpretations," Obama said. "But I don't think that's fooling anybody."
A senior administration official said Obama spoke to German Chancellor Angela Merkel on Tuesday and discussed a potential resolution to the crisis. The Russian-speaking German leader has good relations with the German-speaking Putin, and Berlin is Russia's biggest economic partner.
The official said Obama, in his phone call with Putin last Saturday, had discussed what officials called an "off-ramp" to the crisis in which Russia would pull its forces in Crimea back to their bases and allow international monitors to ensure that the rights of ethnic Russians are protected.
The US president will stay away from a G8 summit scheduled for Sochi, Russia, in June unless there is a Russian reversal in the Ukraine crisis, the official added.
