BRUSSELS (REUTERS) - Russia must be transparent about military exercises along Ukraine's border and not take any steps that could be misinterpreted or "lead to miscalculation during a delicate time," US Defence Secretary Chuck Hagel said on Thursday.

"I'm closely watching Russia's military exercises along the Ukrainian border," Mr Hagel said at a NATO news conference.

"I expect Russia to be transparent about these activities, and I urge them not to take any steps that could be misinterpreted, or lead to miscalculation during a very delicate time - a time of great tension."