A man saving books as a house in the village of Nikolayevka catches fire after a mortar attack on Lugansk suburbs, July 1, 2014. [Photo/IC]

WASHINGTON - The Obama administration on Wednesday threw its weight behind Ukraine's decision to end a ceasefire and resume military operations against the insurgents in the country's east.

White House spokesman Josh Earnest blamed the armed militants for not observing the truce, saying "it only fueled separatist violence and allowed the separatists to make further advances."

Following President Petro Poroshenko's decision to end the 10-day truce Tuesday, the Ukrainian military resumed its offensive in the states of Donetsk and Lugansk by launching air raids on rebel targets.

"We respect the Ukrainian government's decision and its responsibility to maintain public order in their country and to protect the population," Earnest told reporters at a daily news briefing.

He once again urged Russia to take "concrete action" to help de- escalate the conflict in eastern Ukraine.

State Department spokeswoman Jennifer Psaki described Kiev's operations as "moderated and measured," saying "They've been taking steps to maintain calm within their own country."

Russian President Vladimir Putin on Monday threatened to use force in eastern Ukraine to protect the Russian nationals.

"I would like to make it clear to all," he said at a meeting of Russian ambassadors and envoys. "This country will continue to actively defend the rights of Russians, our compatriots abroad, using the entire range of available means -- from political and economic to operations under international humanitarian law and the right of self-defense."

The foreign ministers of Germany, France, Russia and Ukraine met in Berlin, Germany, Wednesday and pledged to take "all necessary measures" and use their influence to achieve a "sustainable" ceasefire in eastern Ukraine.