KIEV, Ukraine -- For two weeks, the mysteriously well-armed, professional gunmen known as "green men" have seized Ukrainian government sites in town after town, igniting a brush fire of separatist unrest across eastern Ukraine. Strenuous denials from the Kremlin have closely followed each accusation by Ukrainian officials that the world was witnessing a stealthy invasion by Russian forces.
Now, photographs and descriptions from eastern Ukraine endorsed by the Obama administration Sunday suggest that many of the green men are indeed Russian military and intelligence forces -- equipped in the same fashion as Russian special operations troops involved in annexing the Crimea region in February. Some of the men photographed in Ukraine have been identified in other photos clearly taken among Russian troops in other settings.
And Ukraine's state security service has identified one Russian reported to be active among the green men as Igor Ivanovich Strelkov, a Russian military intelligence operative in his mid- to late 50s.
He is said to have a long resume of undercover service with the Main Intelligence Directorate of the Russian general staff, most recently in Crimea in February and March and now in and around the eastern Ukrainian city of Slovyansk.
"There has been broad unity in the international community about the connection between Russia and some of the armed militants in eastern Ukraine, and the photos presented by the Ukrainians last week only further confirm this, which is why U.S. officials have continued to make that case," Jen Psaki, the State Department spokeswoman, said Sunday.
Russia's role in eastern Ukraine has a critical bearing on the agreement reached Thursday in Geneva among Russian, Ukrainian, U.S. and European diplomats to ease the crisis. U.S. officials have said that Russia would be held responsible for ensuring that the Ukrainian government buildings were vacated, and that it could face new sanctions if the terms were not met.
The Kremlin insists that Russian forces are in no way involved, and that Mr. Strelkov does not even exist, at least not as a Russian operative sent to Ukraine with orders to stir up trouble.
"It's all nonsense," President Vladimir Putin said Thursday during a four-hour question-and-answer show on Russian television. "There are no Russian units, special services or instructors in the east of Ukraine."
Pro-Russian activists who have seized government buildings in at least 10 towns across eastern Ukraine also deny getting help from professional Russian soldiers or intelligence agents.
But masking the identity of its forces, and clouding the possibilities for international denunciation, is a central part of the Russian strategy, developed during years of conflict in the former Soviet sphere, Ukrainian and U.S. officials say.
John Schindler, a former National Security Agency counterintelligence officer who now teaches at the Naval War College, calls it "special war" -- "an amalgam of espionage, subversion, even forms of terrorism to attain political ends without actually going to war in any conventional sense."
And one country, Mr. Schindler noted in an article last year in which he coined the term, that particularly excels at special war is Russia, which carried out its first post-Soviet war to regain control of rebellious Chechnya back in 1994 by sending in a column of armored vehicles filled with Russian soldiers masquerading as pro-Moscow Chechens.
Russia's flair for "maskirovka" -- disguised warfare -- has become even more evident under Mr. Putin, a former KGB officer whose closest advisers are mostly from that same Soviet intelligence agency.
Meanwhile, the truce reached last week in Geneva was fraying Sunday, when a shootout at a checkpoint run by pro-Russian militants near the town of Slovyansk left at least three people dead.
At around 2 a.m. on a road lined with blossoming apricot trees, four cars drove toward the checkpoint and their occupants opened fire, killing three local men who were standing guard, according to pro-Russian militants who control this town.
It was unclear whether the shooting was an event staged by provocateurs, an accident or an attack on pro-Russian militants. The difficulty in sorting out what happened will resonate far beyond Slovyansk, the linchpin of a string of midsize towns north of the regional capital, Donetsk, that are controlled by pro-Russian militants.
Last week's diplomatic settlement called for illegally armed groups to lay down their weapons, though the chances of this formula for peace succeeding seemed slim from the beginning.
Within hours, pro-Russian militants in eastern Ukraine said they had no intention of disarming in accordance with the agreement, which they did not sign. Russia's Foreign Ministry said the provision calling for disarmament covered "in the first place" the Ukrainian nationalist group Right Sector, which has its base in western Ukraine.
The United States has said it will impose additional sanctions on Russian businessmen, and possibly on a bank or oil company, if the Geneva agreement falls apart. So far, militants have not budged from the buildings they have occupied or handed in their guns.
Ukraine's Foreign Ministry issued a statement Sunday calling groundless the Russian ministry's assertion that the attackers had been members of Right Sector. Right Sector also denied any involvement.