GENEVA (AFP) - Ukraine's ambassador to the United Nations in Geneva warned on Thursday there were signs that Moscow was preparing to launch a large-scale assault in southern and eastern parts of his crisis-hit country.

"There are indications that Russia is braced to unleash a full-blown intervention on Ukraine's east and south," Mr Yurii Klymenko told reporters.

The march by Russian troops and pro-Kremlin militias across Crimea, a mostly Russian-speaking peninsula roughly the size of Belgium, has been unhalting since President Vladimir Putin received his parliament's blessing to use force against the ex-Soviet neighbour following the February 22 fall there of a Moscow-backed regime.

Following Russia's annexation of Crimea, Kiev's new leaders and their Western allies now fear that Mr Putin has set his sights on the Russified southeastern swathes of Ukraine as part of his self-declared campaign to "protect" compatriots there.

Mr Klymenko said the Russian military build-up in Kherson, a Ukrainian province just north of Crimea, indicated a planned onslaught.

He also cited allegations that Russians were laying landmines in the area.

He added that Ukrainian security services had detained individuals with Russian security service IDs for stoking strife across the east and south of the country.

"Ukraine and the Ukrainian people are ready to protect their homeland by all means necessary," Mr Klymenko said, stressing though that "at this stage we are committed to a peaceful solution."

"The use of the right to self-defence would be the last resort for Ukraine," he said.