Leaders of U.S. spy agencies said on Tuesday that Russian President Vladimir Putin may intensify the assault on Ukraine, despite military setbacks and economic hardships resulting from international sanctions, setting up "an ugly next few weeks."

"Our analysts assess that Putin is unlikely to be deterred by such setbacks and instead may escalate," Director of National Intelligence Avril Haines told the annual House of Representatives Intelligence Committee hearing on worldwide threats, where she testified with other intelligence agency directors.

With tensions so high, there is always the potential for "unintended escalation," Haines said.