Ukraine officials vowed Friday to continue a military offensive against pro-Russian rebels in the country's east, after separatists there shot down a helicopter, killing at least a dozen servicemen.
Acting Defense Minister Mykhailo Koval told reporters his forces have completely cleared separatists from the southern and western parts of the Donetsk region, as well as the northern part of the neighboring Luhansk region. He said the mission will continue until peace and order is restored.
But a spokesman for Ukraine's so-called anti-terrorist operation reported fighting took place Thursday night in the restive Luhansk region, which borders Russia.
Speaking to reporters by phone, Vladislav Seleznyov said rebels attacked a Ukrainian military base.
"There is information that the Luhansk military base was besieged by terrorists," Seleznyov told reporters in a conference call. "They made three attempts to capture it ... using Kalashnikovs [rifles], other small arms and grenade launchers."
Koval said more than 20 service members have been killed in eastern Ukraine since the government launched an "anti-terrorist" operation there in mid-April.
Putin calls for halt
Russian President Vladimir Putin on Friday on Ukraine's government to halt its military operation against pro-Russian separatists in eastern Ukraine.
The Kremlin's press service reported Friday that in a phone call with French President Francois Hollande, Putin noted the need for an "immediate termination" of the Kyiv authorities' "violence and bloodshed" and for the start of a "direct dialogue" between Kyiv and southeastern Ukraine,
White House spokesman Jay Carney said Friday that Russian troops appear to be withdrawing from the border area, but that the pullback is not complete. He said the White House does not have confirmation that the movement represents a full withdrawal.
NATO Secretary-General Anders Fogh Rasmussen said Friday that Russia is moving about two thirds of the troops it had close to the Ukrainian border. In a statement, NATO said several thousand troops remain in the area.
U.S. and NATO officials have repeatedly urged Russia to withdraw its troops, saying their presence is raising tensions. There are also reports that fighters are crossing from Russia into Ukraine.
Despite weeks of Kremlin denials, Russia's state-controlled news agency Ria Novosti
said 33 of the estimated 50 rebel fighters killed Monday in Donetsk in a battle with Ukrainian troops came from Russia.
The news agency quoted the prime minister of the self-proclaimed Donetsk People's Republic as saying the bodies of the foreigners have been identified and returned to their relatives.
OSCE monitors detained
Meanwhile, the Organization for Security and Cooperation in Europe (OSCE) says it has lost contact with another four-person group of monitors in eastern Ukraine. The group was last heard from late Thursday. Rebels have been holding four other OSCE observers since late Monday.
Obama - Ukraine
President Barack Obama will meet next week with Ukraine's incoming president to highlight Washington's security commitment to eastern Europe following Russia's annexation of Crimea.
The White House on Friday announced the meeting with President-elect Petro Poroshenko, saying it will take place in Warsaw on the sidelines of 25th anniversary celebrations marking the end of communist rule in Poland. Obama's four-day trip will end June 6 in Normandy on the 70th anniversary of the World War II Allied D-Day landing.
Russian President Vladimir Putin is also set to visit Normandy for memorial services. But the White House said President Obama has no plans to meet directly with the Russian leader, as bilateral tensions simmer over Russia's role in Ukrainian unrest.
Gabe Joselow contributed to this report from Kyiv, Ukraine, and Jeff Seldin contributed from the Pentagon.