Ukraine struggled late Wednesday to regain control of key sections of its border with Russia, after pro-Russian separatists overran a military headquarters in an hours-long battle. A second border post in the eastern city of Luhansk also fell to rebels.



A Ukrainian border guard statement confirmed a retreat from its internal security base, but it said troops had partially redeployed and were "carrying out their tasks." The National Guard said six militants were killed and three Ukrainian troops were wounded in the fighting.



Witnesses, including Western reporters, said Ukrainian forces abandoned the Luhansk base after running out of ammunition. The Associated Press quoted a rebel spokesman as saying the overpowered Ukrainian troops were allowed to flee the nearby border checkpoint.



It also said pro-Russian militia were later seen driving away in the border guards' vehicles.



But also during the last 24 hours, a spokesman for Kyiv’s “anti-terrorist operation” claimed Ukrainian government forces killed more than 300 separatist fighters and wounded at least 500 amid heavy fighting in and around Slovyansk.



Government troops used aircraft, helicopters and artillery against rebels who have controlled the area since April, spokesman Vladyslav Seleznyov said.



Separatists disputed the casualty count.



“Losses to the Ukrainian side were greater than ours,'' Aleksandr Boroday, “prime minister” of the self-proclaimed Donetsk People's Republic, was quoted by Interfax as saying.



Seleznyov said two Ukrainian servicemen had been killed and 45 wounded. The numbers could not be independently confirmed.



Ukraine’s government says the unrest in the country’s east is being instigated and fomented by Russia in response to Kyiv’s turn toward the West.



Recently intensified operations against rebels were ordered by Ukrainian President-elect Petro Poroshenko who, with close to 55 percent of the vote, won a resounding victory in elections May 25.



Possible Putin meeting



Poroshenko said Wednesday he may meet with Russian President Vladimir Putin to address tensions between the two countries when the two leaders will be in France later this week.



“As things stand now, a meeting between me and Putin is not envisaged, but I do not rule out that it could take place in one format or another,” Poroshenko told a news conference in Warsaw after meeting with President Barack Obama and European leaders.



World leaders, including Poroshenko and Putin, will converge on Normandy, France, Friday for a ceremony marking the 70th anniversary of the allied D-Day invasion against Nazi forces in World War II.



Poroshenko said that he was working on a plan to address tensions in eastern Ukraine through a de-centralization of power, a broad amnesty, and elections for local government.



He said he discussed his plan with U.S. and European leaders in Warsaw and that talks on the issue would continue in France.



Poroshenko will formally assume the presidency in Ukraine following his inauguration on June 7.



Reiterating accusations that Russia has a hand in the separatist unrest in eastern Ukraine, NATO's top military commander called on Moscow Wednesday to stop destabilizing the country through the use of Russian-backed forces.



"Russia is continuing to destabilize Ukraine… Russian irregular forces, Russian-backed forces, and Russian financing are very active in eastern Ukraine. This has to stop,'' U.S. General Philip Breedlove, NATO's supreme allied commander Europe told reporters on the sidelines of a meeting of NATO defense ministers in Brussels.



Breedlove said that Russia’s influence in the events in eastern Ukraine is “very clear,” and called Moscow’s effort “very well-led, very well-financed [and] very well-organized."



Commenting on Russia’s continued troop presence on its border with Ukraine - previously estimated by NATO at 40,000 - Breedlove said that despite Moscow’s pledged withdrawal, several large formations remain and appear not to have reduced their presence in any way.



Moscow denies involvement in eastern Ukraine.



US security assistance



The United States has offered Ukraine an additional $5 million in non-lethal assistance to help the country's military forces in their effort to battle pro-Russian separatists in eastern Ukraine.

US Security Assistance to Ukraine