NATO: Russia removing troops

"We have seen some signs of a start of Russian withdrawal," outgoing NATO Secretary General Anders Fogh Rasmussen said Friday at a meeting of the Western military alliance's Parliamentary Assembly in the Lithuanian capital Vilnius. "Maybe around two thirds have now pulled back."

US Secretary of State John Kerry had earlier said Russia's troops along the Ukraine border, which NATO estimated to number around 40,000, were being withdrawn. Russian President Vladimir Putin had earlier said the soldiers would return to base when spring exercises had ended.

Despite the troop pull back, however, Rasumussen said Russia still had a substantial military force along its border with Ukraine that could intervene if ordered to do so by Moscow.

"We welcome what we have seen but we continue to urge Russia to pull back all troops from the Ukrainian border," he said.

Rasmussen also announced NATO's 28 ambassadors would meet with their Russian counterpart in Brussels on Monday. The meeting will be the first since Moscow's annexation of Ukraine's Crimean Peninsula on March 5, a move that sparked an armed uprising in the east and the worst diplomatic tension with the West since the end of the Cold War.

In Washington, White House Deputy National Security Advisor Ben Rhodes told reporters Friday that President Barack Obama will meet with Ukraine's new President-elect Petro Poroshenko next week. The visit, set to take place on Wednesday, is part of Obama's European visit aimed at reassuring allies about Russian aggression in Ukraine.

OSCE observers detained

Earlier on Friday, the Organization for Security and Co-operation in Europe (OSCE) announced that another group of its civilian observers had been detained by gunmen in eastern Ukraine. The four observers and their Ukrainian translator were stopped in Sievierodonetsk, around 100 kilometers (60 miles) north of Luhansk, on Thursday evening.

Four other OSCE monitors were detained by pro-Russian separatists in the neighboring Donetsk region on Monday, and remain missing. The self-declared mayor of the separatist stronghold of Slovyansk, Vyacheslav Ponomaryov, has said that the four had been detained by his men on suspicions of spying.

Meanwhile, Ukraine's acting defense minister said the country will continue its armed offensive against separatists.

"Our task is to bring peace and order to the region," Mykhailo Koval said Friday, adding military operations would keep going "until these regions begin to live normally, until there is peace."

Koval's statement came a day after pro-Russian separatists shot down a Ukrainian military helicopter near Slovyansk, killing 12 servicemen. It was the deadliest loss of life for government troops since 18 were killed on May 22 around Donetsk.

Russian interference accusations

Amid the heightened tension on Friday, Rasmussen urged Russia to stop interfering in the region - an accusation Russia flatly denies.

"We continue to call on Russia to stop supporting armed pro-Russian gangs and seal the border, so that we don't see arms and fighters crossing into Ukraine," he said, adding that NATO would increase its cooperation with Ukraine.

"You will see in the future a strengthened cooperation between NATO and Ukraine, also when it comes to the military cooperation," Rasmussen said.

dr/pfd (dpa, AFP, Reuters, AP)