Russian Foreign Minister Sergei Lavrov met his Ukrainian counterpart on Monday for crisis talks on the sidelines of a nuclear summit in The Hague, the Russian foreign ministry said.

The ministry posted a photograph on its website of Lavrov meeting Ukraine's interim Foreign Minister Andriy Deshchytsya for the first time since the Kremlin's seizure and annexation of the Crimea peninsula.

Russia on Monday redrew its official maps to include Crimea after annexing the peninsula, even though the move has not been internationally recognized.

Maps on the Kremlin and government websites include Crimea, describing it as the "youngest region of Russia."

There will be no G8 summit in Russia this year following the crisis in Ukraine, British Prime Minister David Cameron said on Monday, ahead of a meeting of G7 leaders in The Hague.

"We should be clear there's not going to be a G8 summit this year in Russia. That's absolutely clear," Cameron told British television.

The White House is "very concerned by the potential for escalation" after Russia massed its troops on the border with Ukraine, a close aide to U.S. President Barack Obama said Monday.

"We are watching very closely, we believe that Russia stands an enormous amount to lose" from any escalation, Deputy National Security adviser Ben Rhodes told journalists as leaders gathered in The Hague to discuss a response to the crisis.

Russia said Monday it had banned entry to the country for 13 Canadian lawmakers and public figures, after Canada imposed sanctions against seven Russian and three Crimean senior officials over the crisis in Ukraine.

The Canadians now refused entry to Russia include Prime Minister Stephen Harper's foreign policy adviser Christine Hogan, parliament speaker Andrew Sheer and journalist turned politician Chrystia Freeland, the foreign ministry said in a statement.

Russian authorities on Monday reimposed an avalanche warning for the mountain resort used to host the Sochi Winter Olympic and Paralympic Games events, after an avalanche killed two women in the area at the weekend.

The avalanche hit the Rosa Khutor complex used for the Olympic and Paralympic Alpine events, killing a teenage girl and a woman, at around noon on Sunday, regional investigators said Monday.

Romania's president said Monday NATO should reposition its forces after Russia's annexation of Crimea.

Traian Basescu said he would discuss the crisis in Ukraine, which shares a border with Romania, with world leaders meeting in The Hague.

Ukraine on Monday ordered its outnumbered troops to withdraw from Crimea after Russia's lightning annexation of the peninsula as world leaders met for emergency talks on the worst East-West standoff since the Cold War.

The dramatic announcement came after Ukraine lost yet another base in Crimea and as world leaders gathered in The Hague for a security summit set to be dominated by concerns over the Ukraine crisis.

Russia's deputy defense minister Anatoly Antonov denied on Sunday it was massing troops on the Ukrainian border, saying it was observing international agreements.

"The Russian defense ministry is observing all the international agreements on limiting the numbers of troops in regions bordering Ukraine," Antonov told journalists, cited by the Interfax news agency.

President Barack Obama opens a six-day trip to Europe and Saudi Arabia on Monday seeking to reassure U.S. allies amid the worst East-West crisis in years and to defend his nuclear diplomacy with Iran.

A visit to the third Nuclear Security Summit in The Hague -- which grew out of Obama's initiative to prevent the spread of weapons of mass destruction and radioactive material -- has been planned for months.