(Adds incident at border post, background)

KIEV, March 3 (Reuters) - Russian forces began moving troops into Ukraine's Crimea region by ferry on Monday after seizing control of the border post on the Ukrainian side of the waterway, Ukraine's border guards said.

Russians who seized the isolated Black Sea peninsula have been surrounding the ferry terminal for days but until now had not taken control of Ukraine's border guard station.

A border guard spokesman said Russian troops seized the checkpoint after the border guards tried to stop two buses carrying seven armed men, and the next ferry brought three truckloads of soldiers across.

Earlier on Monday, the Ukrainian border guards said they had seen Russia assembling an armoured column on its side of the 4.5 km (2.7 mile) wide Kerch strait that separates the Crimea peninsula from southern Russia.

Russian troops have seized Crimea and President Vladimir Putin has declared Moscow has the right to intervene in Ukraine to protect Russian citizens in Ukraine, sparking the biggest crisis between Russia and the West since the Cold War. (Editing by Janet Lawrence)

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