London: Nearly aweek after a ceasefire was supposed to have gone into effect in Ukraine, United States Secretary of State John Kerryhas mooted the imposition of additional sanctions because of what he has called Russia's "brazen" violations of the agreement.

"We know to a certainty what Russia has been providing and no amount of propaganda is capable of hiding these actions," Mr Kerry said, using particularly strong language. "We're not going to sit there and be part of this kind of extraordinarily craven behaviour at the expense of the sovereignty and integrity of a nation."

Ukrainian soldiers ride on a tank near Artemivsk in eastern Ukraine on Saturday. Credit:Reuters

Moscow has denied accusations that its forces are fighting in Ukraine.

MrKerry told reporters that "more serious sanctions" were being weighed.