Russian President Vladimir Putin on Tuesday told troops to return to their permanent bases after calling a snap drill to check their battle-readiness last week.

"The commander-in-chief President Vladimir Putin gave the order to the troops and units taking part in military exercises to return to their permanent bases," Putin's spokesman Dmitry Peskov told Russian news agencies.

U.S. Secretary of State John Kerry took another swipe at Russia on Monday, saying that Moscow "has put pressure on Moldova," as he backed the former Soviet state in seeking closer ties with the West.

Kerry, who has lambasted Russia over its military actions in Ukraine, another former Soviet state and neighbor, was speaking after meeting in Washington Moldovan Prime Minister Lurie Leanca, who is seeking closer ties with the European Union.

Russian troops and military planes were flowing into Crimea on Monday in violation of accords between the two countries, Ukrainian border guards said, as Moscow reportedly warned Ukrainian forces in Crimea to surrender or face a confrontation.

The Interfax news agency quoted a Ukrainian defense ministry source as saying that “the Russian fleet has given Ukrainian forces in Crimea a 12-hour ultimatum to surrender or face a storm."

The U.S. and Russian foreign ministers will attend French-sponsored talks in Paris Wednesday on helping Lebanon cope with the conflict in Syria, but the talks look set to be overshadowed by the Ukraine crisis, France said.

U.S. Secretary of State John Kerry was scheduled to come for the meeting of the International Support Group for Lebanon meeting but French Foreign Minister Laurent Fabius said Monday that Russia's Sergei Lavrov would also attend the conference.

Ukraine's deposed president Viktor Yanukovych is still the legitimate head of state of the country even if his authority is "negligible", Russian Prime Minister Dmitry Medvedev said Monday.

Medvedev added that Russia does not recognize the new authorities who took power in Kiev after the overthrow of Yanukovych, saying they had violated the constitution.

Russia's Vladimir Putin has agreed to a proposal from Angela Merkel to set up a contact group on Ukraine, the German government said Sunday.

The German chancellor put the proposal to Putin in a telephone conversation late Sunday in which she also "accused the Russian president of violating international law with the unacceptable Russian intervention in Crimea," said a government statement.

NATO allies on Sunday urged the deployment of international observers to Ukraine and said the alliance sought "to engage" with Moscow at NATO-Russia talks.

"We urge both parties to immediately seek a peaceful resolution through dialogue, through the dispatch of international observers under the auspices of the United Nations Security Council or the OSCE," said a statement issued after almost eight hours of talks between NATO's 28 ambassadors.

U.S. Secretary of State John Kerry bluntly warned Russia Sunday that it risked losing its seat among the prestigious Group of Eight nations, as well as economic turmoil and sanctions, over the Ukraine crisis.

The top U.S. diplomat hit the Sunday talk shows to ratchet up pressure on Moscow, after he convened a crisis conference call with European and Canadian foreign ministers and President Barack Obama held a 90-minute phone call with Russian counterpart Vladimir Putin Saturday.

Pope Francis on Sunday called on all sides in Ukraine to overcome "incomprehension" and appealed to the international community to promote dialogue.

"I ask you again to pray for Ukraine, which is experiencing a delicate situation," Francis said in his weekly Angelus blessing from a window of the Vatican Apostolic Palace overlooking St Peter's Square.

Moscow police on Sunday arrested dozens protesting against military intervention in Ukraine after President Vladimir Putin won approval from senators to send in troops to the crisis-hit country.

Police said 40 people were detained for "attempts to violate public order" at a protest near the defense ministry in central Moscow, the Interfax news agency said.