Russian President Vladimir Putin has shunned an invitation to attend a Nato summit with US President George W. Bush in Turkey this month, a senior Nato diplomat said on Wednesday.
"We are told that he's not intending to come. Foreign Minister (Sergei) Lavrov will be coming," the diplomat said.
Nato spokesman James Appathurai said discussions were still going on with Moscow, and the 26-member alliance had not been officially notified whether Putin would attend.
But the diplomat said: "As definitely as anything ever is, he's not coming. I think Putin judged there wasn't enough in it for him to come".
The disclosure was another blow to an event for which ambitions have already been scaled down with the decision not to invite Arab states, and with no prospect of an agreement to a direct military role for Nato in Iraq.
One possible factor was that Nato would be celebrating the recent accession of seven new eastern European members, including the former Soviet Baltic republics whose membership of Moscow's former Cold War adversary has irked Russia.
Nato aircraft began patrolling the skies over Estonia, Latvia and Lithuania on March 29 as soon as the three countries, along with Bulgaria, Romania, Slovakia and Slovenia, joined the alliance, joining the former Warsaw Pact states admitted in 1999 - Poland, the Czech Republic and Hungary.
But diplomats said Nato's enlargement was probably not the showstopper for Putin. Indeed, he sent Lavrov to Nato for talks in April just hours after the flags of the seven former communist states had been raised at the alliance's headquarters.
Vladimir Socor, a senior fellow of the Washington-based Jamestown Foundation, wrote in the Wall Street Journal last week that Putin was "playing hard to get" to win concessions in a stand-off on the treaty limiting conventional forces in Europe.
He said Putin's conditions for coming to Istanbul included continuing tolerance of Russia's failure to comply with commitments under the 1999-adapted Treaty on Conventional Forces in Europe (CFE).
Signed in the dying days of the Cold War, the treaty limits military equipment deployed and stored between the Atlantic Ocean and Russia's Ural mountains.
Russia is anxious for the adapted treaty to be ratified so that the Baltic states can sign up. Some Russian officials fear they could become Nato outposts for nuclear arms or army bases.