US President Barack Obama speaks during a joint press conference with his Estonian counterpart at the Bank of Estonia in Tallinn, Estonia, on September 3, 2014. US President Barack Obama arrived in Estonia to meet Baltic leaders and reaffirm Washington's commitment to the security of ex-Soviet NATO members. AFP PHOTO / SAUL LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images) President Barack Obama has slowed deportations by nearly 20 percent. (Photo: SAUL LOEB/AFP/Getty Images)

TALLINN, Estonia (CBS News/CBSDC/AP) — President Barack Obama proclaimed an unwavering and permanent U.S. commitment to the security of its NATO allies, as he mounted a show of solidarity Wednesday with European nations anxious about Russia’s aggression in Ukraine.

During a visit to Estonia, Obama also announced the U.S. would send more Air Force units and aircraft to the Baltics, and called Estonia’s Amari Air Base an ideal location to base those forces.

Standing shoulder to shoulder with Estonian President Toomas Hendrik Ilves, Obama ticked through a list of U.S. military resources already at work in the region, and said the U.S. has a duty under the NATO charter to the alliance’s collective defense.

“It is unbreakable, it is unwavering, it is eternal. And Estonia will never stand alone,” Obama said in Tallinn, Estonia’s port capital.

Obama’s firm words came as NATO nations were preparing to commit to a more robust rapid-response force for the region, in response to Russia’s incursion in Ukraine. Moscow’s moves have sparked fears among member states on NATO’s eastern flank that they could be Russian President Vladimir Putin’s next target.

Yet shortly after Obama arrived in Europe, the office of Ukrainian President Petro Poroshenko said he and Putin had reached agreement on a cease-fire — an unexpected development that added further uncertainty to Obama’s meetings with regional leaders.

Obama said it was too early to tell what the cease-fire meant. He noted previous unsuccessful attempts and questioned whether pro-Russian separatists would abide by any cease-fire.

“We haven’t seen a lot of follow-up on so-called announced cease-fires,” Obama said at a news conference with Ilves. “Having said that, if in fact Russia is prepared to stop financing, arming, training, in many cases joining with Russian troops, activities in Ukraine and is serious about a political settlement, that is something we all hope for.”

Ilves, reacting to word of the cease-fire, said wryly, “I just hope it works.”

The Estonian leader cautioned that for a cease-fire to be successful, Russia would have to acknowledge its own participation in the conflict – a step Moscow has previously refused to take. After a meeting with Ukrainian President Petro Poroshenko last week, Putin had said a cease-fire was not discussed because Russia was not a party to the conflict.

“This is aggression,” Ilves said. “Russia must admit that it is a party to the conflict.”

He called for “a robust and a visible ally presence here in Estonia,” arguing that such a presence would be the best way to deter any potential aggressors in the region – a clear reference to Russia.

And after the announcement from Poroshenko’s office Wednesday, a Putin spokesman denied any accord had been reached, asserting — again — that Moscow isn’t a party to the hostilities in Ukraine.

Also, the Reuters news agency reports that a pro-Russia rebelleader in the Donbass region of eastern Ukraine said Wednesday the withdrawal of Ukrainian forces from “our territory” was the main condition for peace in the separatist-held area.

According to Reuters, Vladimir Antyufeyev, deputy prime minister of the self-proclaimed Donetsk People’s Republic, told it by phone that talk of a Russia-Ukraine truce was a “provocation” because Russia isn’t a party to the conflict.

At the news conference, Obama held up Estonia as an example of how every member of the military alliance needs to do its fair share for the collective defense of all 28 members. The U.S. and Estonia are two of four NATO countries that fulfill their pledges to contribute 2 percent of their GDP to defense spending.

Later Wednesday, Obama and Ilves were to hold broader security talks that include the leaders of Latvia and Lithuania. Then Obama departs for Wales, where a two-day NATO summit will begin on Thursday.

NATO allies plan to agree during the summit to a stepped-up response to Russia, including the rapid response force, which will involve positioning more troops and equipment in the Baltics and elsewhere in Eastern Europe. It’s unclear whether the plan will satisfy the concerns of the Baltic nations, who have been pressing NATO for permanent bases in the region.

After arriving in Tallinn on a crisp and sunny morning, Obama was greeted by Ilves at Kadriorg Palace, where Obama placed his hand over his heart as the U.S. national anthem played. The two leaders then inspected Estonian troops and shook hands with groups of flag-waving schoolchildren.

Obama becomes the second sitting American president to visit Estonia, following President George W. Bush, who traveled here in 2006. As he entered the palace, Obama wrote in a guest book that it was an honor to visit “a nation that shows what free people can achieve together.”

The Baltics were invaded by the Soviet Union and Nazi Germany during World War II. After the Soviet Union crumbled, the Baltic countries turned to the West and joined the European Union and NATO in 2004, much to the chagrin of Russia.

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