US Director of National Intelligence Avril Haines tells a Senate hearing the next few months could see Russian actions escalate and become more unpredictable.
She warns Russia could seek a land bridge to the breakaway Moldovan territory of Transnistria.
“The current trend increases the likelihood that President Putin will turn to more drastic means,” Haines says.
Meanwhile, the bodies of 44 civilians have been found in the rubble of a collapsed building in the Ukrainian city of Izyum.
Thousands more civilians have also died in Ukraine during the war than previously estimated, the UN human rights monitoring mission in the country says.
There are more than 1,000 troops trapped in the plant, including hundreds who are injured, the Ukrainian deputy PM also says.
Source: BBC news