Russian President Vladimir Putin has declared a relatively modest income of just over $100,000 for last year -- the lowest of all of his staff in the Kremlin, official figures showed Friday.

Putin earned about 3.7 million rubles ($104,000, 75,000 euros) and owns three Russian-made cars, a 77 square-meter flat, a garage and a plot of land, according to a declaration of assets published on the Kremlin's website.

President Vladimir Putin on Thursday sent a letter to leaders of 18 European countries, warning them Russia could cut gas supplies to Ukraine, but suggesting that Moscow and Brussels work together to help restore the ex-Soviet country's battered economy.

If Ukraine does not settle its 1.6 billion euro ($2.2 billion) energy bill, natural gas giant Gazprom would be "compelled to switch over to advance payment for gas deliveries, and in the event of further violation of the conditions of payment, will completely or partially cease gas deliveries," Putin wrote in the letter.

Russian President Vladimir Putin has ordered a crackdown on "destructive" non-government organizations, saying such groups were behind the mass protests that brought down Ukraine's government.

Moscow has repeatedly accused the new authorities in Kiev and the protesters who toppled pro-Moscow President Viktor Yanukovych of being extremists, nationalists and even "Nazis".

The Communist Party won a surprise victory against President Vladimir Putin's ruling party in a mayoral race in Russia's third largest city of Novosibirsk, election officials said on Monday.

Communist lawmaker Anatoly Lokot won 43.75 percent of the vote against the acting mayor Vladimir Znatkov from the ruling United Russia party, who took 39.57 percent, the Siberian city's electoral commission said.

NATO Secretary General Anders Fogh Rasmussen said Tuesday the Western alliance had suspended all military and civilian cooperation with Russia over the crisis in Ukraine, but that political dialogue remained open.

"We are suspending all practical cooperation with Russia, military and civilian," Rasmussen said at a NATO foreign ministers meeting on the crisis in Ukraine, adding however that "diplomatic lines of communication" remained open in the NATO-Russia Council.

Russian President Vladimir Putin informed German Chancellor Angela Merkel on Monday about the partial withdrawal of troops he ordered from a region on the border with Ukraine, her office said.

"Moreover the two discussed further possible steps to stabilize the situation in Ukraine and Transdniestr," Moldova's largely Russian-speaking breakaway region, Merkel's spokesman Steffen Seibert said in a statement.

Russian President Vladimir Putin wants to carry on the frequent "tough but constructive" contacts he has had with Chancellor Angela Merkel on the Ukraine crisis, his spokesman has told German TV.

Dmitry Peskov told ZDF television that the telephone talks between Putin and Merkel were worth their "weight in gold", according to excerpts released ahead of broadcast on "Berlin Direkt" later Sunday.

Russian President Vladimir Putin called his American counterpart Barack Obama Friday to discuss a U.S. proposal for a diplomatic end to the Ukraine crisis while insisting to the United Nations that Moscow had "no intention" of further military action.

The White House said Putin phoned Obama following a bid presented to Russian Foreign Minister Sergei Lavrov by U.S. Secretary of State John Kerry earlier this week.

U.S. President Barack Obama in an interview aired Friday said Russia must "move back" its troops from the Ukraine border and start negotiating.

Obama told CBS News that Russian President Vladimir Putin's decision to assemble forces on the border may "simply be an effort to intimidate Ukraine, or it may be that they've got additional plans."

Japan is to give up to $1.5 billion in financial aid to Ukraine, the government in Tokyo confirmed Tuesday, as the club of rich nations booted Russia off the membership list.

Prime Minister Shinzo Abe announced the figure as he and fellow world leaders, including U.S. President Barack Obama, cancelled an upcoming G8 meeting in Sochi, and said it would be replaced by a G7 event that did not involve Moscow.