Alexei Pushkov, a leading Russian MP, was addressing about 100 MEPs in the parliament's foreign affairs committee.

He was speaking after President Barack Obama said he had not ruled out sending arms to Kiev if diplomacy failed.

The option of lethal defensive weapons was being examined, Mr Obama said.

Mr Pushkov, who is on the US sanctions blacklist, warned that American weapons could "expand the war and turn it into a real threat to the whole European security system", Tass news agency quoted him as saying.

He is not on the EU list of top Russian politicians and industrialists subject to a visa ban and asset freeze, imposed after Russia's annexation of Ukraine's Crimea peninsula in March 2014.