Two U.S. senators are warning that Russian President Vladimir Putin is stalling on peace while preparing a fresh military offensive against Ukraine.

By Guy Faulconbridge and Max Hunder MOSCOW/KYIV (Reuters) -On the eve of peace talks, Ukraine and Russia sharply ramped up the war with one of the biggest drone battles of their conflict, a Russian highway bridge blown up over a passenger train and an ambitious attack on nuclear-capable bombers deep in Siberia.