The European Union said Thursday the Ukrainian government has the right to defend its sovereignty, but urged all sides to focus on easing the crisis.
As Russian President Vladimir Putin warned that Kiev military operations in eastern Ukraine would have "consequences", Brussels said all efforts must be made to implement last week's Geneva accord.
"We have full confidence in the Ukraine government to implement the Geneva accord," said EU foreign affairs chief Catherine Ashton's spokesman Michael Mann.
"We recognise Ukraine's right to take legitimate action to defend its sovereignty and territorial integrity."
Mann said all parties to the Geneva accord -- Brussels, Washington, Moscow and Kiev -- should "do their utmost (so) that the situation is de-escalated."
He pointed out that the parties had committed to "use their influence" to disarm militias and help restore government control over buildings and areas they have seized.
"Recent events do indicate that in certain cases ... not everybody is determined to follow up" the accord, he said, adding that a diplomatic solution was the only way forward.
Asked about the prospect of tougher sanctions against Moscow if the crisis worsens, Mann said the EU was working on possible new measures but their imposition depended on events on the ground.
"There are no hard and fast deadlines," he said.
The European Union has so far imposed visa bans and asset freezes on nearly 40 Ukrainian and Russian officials and business leaders, including members of Russian President Putin's inner circle.
EU leaders have also agreed to study tougher measures, including outright economic measures, but divisions within the bloc have so far held up a decision.