WASHINGTON - Russia's Vladimir Putin won't be on the guest list when President Barack Obama and other world leaders assemble in Germany this week, as part of the punishment for alleged Kremlin-supported aggression in Ukraine.

Yet the Russian president remains a central player in international affairs, including the U.S.-led nuclear talks with Iran, even with the pledge by Western leaders to try to isolate Putin while the crisis in Ukraine persists.

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

U.S. officials say the engagement is 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.

Some analysts say the West risks sending mixed signals to Ukraine, where the government has been pushing for more support. Matthew Rojanksy, a Wilson Center expert on the former Soviet states, 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 Russia later annexed.

The West doesn't recognize that move. But the U.S. and Europe largely have given up on Russia's returning the area to Ukraine. Instead, the West has focused on Moscow'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 violated repeatedly.

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 big global player. He has 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 is the Russian economy. The ruble has stabilized after a dramatic freefall last year that was attributed to both falling oil prices and the West's economic penalties. Still, Russia's economy remains shaky.

It appears unlikely, however, that the U.S. and Europe will toughen sanctions without a major increase in Russian aggression. European nations with 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."