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.

Russia launched an all-out propaganda campaign Sunday to whip up support for possible military action in Ukraine, as state media and ruling party officials claimed armed marauders were terrorizing the ex-Soviet nation.

Kremlin-controlled media launched a full-scale operation with footage aimed at discrediting the new Kiev authorities and rousing anger at alleged outrages perpetrated against the Russian-speaking population.

Ukraine's navy chief announced Sunday he had switched allegiance to the pro-Russian authorities of the flashpoint peninsula of Crimea, a day after he was appointed to the post by interim leader Oleksandr Turchynov, as Ukraine warned it was on the brink of disaster and called up all military reservists.

"I swear to execute the orders of the (pro-Russia) commander-in-chief of the Autonomous Republic of Crimea," Denis Berezovsky said in a televised statement from inside the Crimean headquarters of the Russian Black Sea Fleet, adding that he "swears allegiance to the residents of the Autonomous Republic of Crimea."

U.S. President Barack Obama met with his national security team Saturday to weigh policy options after Russia's parliament endorsed military action in Ukraine, a White House official said.

Senior members of the Washington national security establishment, including General Martin Dempsey, chairman of the Joint Chiefs of Staff, were earlier seen heading into the White House for the rare Saturday meeting.

Greek Foreign Minister Evangelos Venizelos, whose country currently holds the European Union presidency, will travel to Ukraine on Sunday, the Italian news agency ANSA reported in an interview with the minister.

Venizelos will first travel to the city of Mariupol on the Sea of Azov near Crimea, where there is a large ethnic-Greek community, and then to Kiev, it said.

Time was, overturning a freely-elected government would have earned a sharp U.S. rebuke. But as people power revolts sweep some countries, Washington is increasingly giving its blessing to ousting leaders accused of betraying democracy.

From Egypt, where the nation's first democratically-elected president Islamist leader Mohammed Morsi was toppled in July by the army, to Ukraine where Viktor Yanukovych, brought to power in 2010 polls, fled his post after months of street protests, the U.S. has had to fine-tune its response.

No sooner had deadly violence died down in Kiev last week than a menacing video appeared on YouTube, promising a "Great Ukrainian Reconquista" against images of armored vehicles on fire and violent police beatings.

Meet Pravy Sektor, a far-right paramilitary group that rose to prominence during the anti-government protests that rocked Ukraine, prompting warnings that a largely peaceful protest movement had been hijacked by radical elements that could have a major say in politics following the ouster of president Viktor Yanukovych.

EU foreign policy chief Catherine Ashton urged Russia on Saturday to refrain from deploying its armed forces in Ukraine and to abide by international law.

"I deplore today's decision by Russia on the use of armed forces in Ukraine," she said in a statement. "This is an unwarranted escalation of tensions.

The U.N. Security Council will meet Saturday for a second round of emergency consultations, officials said, after Russia's parliament approved the deployment of troops to Ukraine.

The president of the Security Council, currently Luxembourg, invited members to "informal consultations" at 1900 GMT, a statement said.