Ukrainian police shot dead a far-right nationalist leader in the western city of Rivne in a shootout that erupted when they tried to arrest him, the interior ministry said Tuesday.

Oleksandr Muzytchko, head of the Pravy Sektor (Right Sector) in the west of the crisis-hit country, opened fire on the police who shot back, deputy interior minister Volodymyr Evdokimov said, cited by Interfax news agency.

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.

The G7 group of top economic powers on Monday scrapped a planned meeting to be hosted by Russia as they sought to deepen Moscow's isolation over the Ukraine crisis.

After emergency talks on the Ukraine crisis called by U.S. President Barack Obama, the G7 said they would hold a meeting in Brussels without Russia instead of the wider G8 summit that was to have taken place in Sochi.

Just a year ago, Ruslan, a marine in Ukraine's top battalion stationed in the Crimean port of Feodosiya, helped Russian soldiers paint their armored personnel carrier for a military parade.

On Monday, he spotted the same vehicle being used to block the gate to his base as Russians showered its barracks with tear gas and stun grenades in a pre-dawn raid that took the unarmed Ukrainians by complete surprise.

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.

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.