WASHINGTON (AP) — When President Barack Obama and other world leaders gather in Germany next week, Russia's Vladimir Putin will be left off the guest list, part of his punishment for more than a year of alleged Kremlin-supported aggression in Ukraine.

But despite vows from Obama and his European counterparts to isolate Putin as long as the crisis in Ukraine remains unresolved, the Russian leader is still a central player in major international affairs, including the U.S.-led nuclear talks with Iran.

Just this month, German Chancellor Angela Merkel traveled to Moscow for talks with Putin and Secretary of State John Kerry went to Sochi to confer with the Russian leader. Putin and British Prime Minister David Cameron also spoke by phone in recent days and agreed to resume talks aimed at ending Syria's civil war, another matter where Putin's cooperation is crucial.

U.S. officials defend the engagement with Russia, saying it's limited to areas where Moscow and the West have shared interests. Outreach to Putin on such matters, officials argue, should not be seen as a sign that the West has accepted the status quo in Ukraine, where pro-Russian separatists continue to stoke instability.

"It makes sense to cooperate where there is a clear mutual interest as long as you're not being asked to back off matters of principle that matter to the security and well-being of your country and your allies and your friends," Vice President Joe Biden said Wednesday.

However, some regional analysts say the West risks sending mixed signals to Ukraine, where the government been pushing for more support. Matthew Rojanksy, an expert on the former Soviet states at the Wilson Center, said there is "growing disappointment" in Ukraine about what officials there see as the West's "pale commitment" to protecting its sovereignty.

"They are all deeply worried that the United States will throw them under the bus to make a grand bargain with Putin," Rojanksy wrote in an email from Kiev, where he was meeting with government officials and civil society groups.

The conflict between Russia and Ukraine escalated last year when the Kremlin-backed president in Kiev fled amid protests. Pro-Russian separatists moved to take over the strategically important Crimean Peninsula, which was then formally annexed by Russia.

While the West doesn't recognize the annexation of Crimea, the U.S. and Europe have largely given up on Russia returning the area to Ukraine. Instead, the West's focus has been on Russia's threatening moves in eastern Ukraine, the site of months of clashes between government forces and rebels that Kiev says are backed by Moscow. A fragile cease-fire agreed to in February has been repeatedly violated.

The West wielded the threat of diplomatic isolation as a punishment for Russia based in part on the belief that Putin values being seen as a major player on the world stage. The Russian leader has instead tried to use the West's actions to bolster Russian nationalism and his own popularity at home.

On Thursday, Putin suggested that the U.S. corruption investigation into soccer's governing body was part of an attempt to take the 2018 World Cup away from Russia. He also accused the U.S. of seeking to "illegally persecute" people.

The West's clearest pressure point for getting Putin to change his behavior in Ukraine is the Russian economy. The ruble has stabilized after a dramatic freefall last year that was attributed to both falling oil prices and Western economic sanctions. Still, Russia's economy remains shaky.

It appears unlikely, however, that the U.S. and Europe will ramp up sanctions without a major increase in Russian aggression. European nations that have strong financial ties with Russia fear the sanctions could damage their own economies.

When Obama meets with European leaders at next week's Group of Seven summit in Germany, he is expected to press them to renew sanctions set to expire this summer. Russia was invited to join the G-7, a bloc of leading industrial nations, in 1998 and remained a member of what was then called the G-8 until last year when the original members suspended its participation in retaliation for its actions in Ukraine.

Heather Conley, a Europe expert at the Center for Strategic and International Studies, said that one of the risks for the West in deepening engagement with Putin while the crisis in Ukraine continues is that the Russian leader may start to think he can simply wait out the U.S. and Europe's attention span.

"We're really stuck," she said. "Mr. Putin is not going to come to his senses. This is a long-term challenge."

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