Russian President Vladimir Putin on

Russian President Vladimir Putin on Monday signed a decree recognising Crimea as an independent state following a weekend referendum to secede from Ukraine and join Russia in a move that has fanned the worst East-West crisis since the Cold War.

"It's deplorable that Russia recognised the independence of the Autonomous Republic of Crimea, a move that violates Ukraine's sovereignty and territorial integrity," the Japanese foreign ministry said in a statement Tuesday.

"Japan will suspend negotiations on easing visa requirements, and will not begin talks on a new investment accord, an outer space accord and an accord aimed at preventing risky military activities," it added, without elaborating.

The United States and Europe announced sanctions on Monday, with the White House saying the measures, the toughest against Russia since the Cold War, would target economic power brokers in Moscow if the Kremlin does not change course.

There was no sign of Putin backing down, however, and Crimea's pro-Moscow authorities made plans to swiftly honour Sunday's 96 percent referendum vote to return to the Russian fold.

"Japan urges Russia to understand the position held by the G7 (Group of Seven)" world powers, including Japan, Chief Cabinet Secretary Yoshihide Suga told reporters.

Suga, the top government spokesman, added that Japan "is, of course, thinking" about further action against Russia. He did not supply details.

However, Suga disputed suggestions that Tokyo's apparent lukewarm sanctions -- compared with its western partners' travel bans and asset freezes against Russian and Ukraine officials -- are linked to efforts aimed at solving a decades-old territorial disputes with Moscow.

"That's not the case," he said. "Japan never overlooks an attempt to change the status quo through force.