Moscow’s dual campaign of intensified frontline attacks and bombardment of Ukrainian cities has further reduced the prospects for an end to the fighting.

The warnings over the offensive come as a U.S.-brokered peace process has limped along with inconclusive meetings and little concrete results.

KYIV (Reuters) -Ukrainian President Volodymyr Zelenskiy has said that Russia has gathered 50,000 troops near Ukraine's northern Sumy region, but added that Kyiv had taken steps to prevent Moscow from conducting a large-scale offensive there.