NATO's secretary-general warned Moscow on Sunday it was threatening peace in Europe with its seizure of Crimea and should "de-escalate tensions", but diplomats said the alliance was unlikely to agree on major steps to rein Russia in.
Speaking moments before chairing an emergency meeting of NATO ambassadors, Anders Fogh Rasmussen warned that Russia's actions in Ukraine could destabilize the continent.
"What Russia is doing now in Ukraine violates the principles of the United Nations charter," Rasmussen told reporters before a meeting of the North Atlantic Council, made up of the permanent representatives to the 28-nation military alliance.
"It threatens peace and security in Europe. Russia must stop its military activities and its threats."
Despite the strong words, diplomats said they did not expect NATO to agree on significant measures to pressure Russia, with the West struggling to come up with a forthright response that does not risk pushing the region closer to military conflict.
The stand-off has created the greatest moment tension between Russia and the West since the collapse of the Soviet Union in 1991, an event Russian President Vladimir Putin has described as the geopolitical catastrophe of the 20th century.
"Don't expect big decisions," said one NATO ambassador.
Another diplomat to the military alliance added: "I think we must be careful not to give the Russians anything that could rile up pro-Russian sentiment in Crimea."
Despite a 90-minute phone call between President Barack Obama and Putin on Saturday, and other calls to the Kremlin by European leaders, Russia shows no sign of backing away from its de facto occupation of Crimea and presence in east Ukraine.
U.S. Secretary of State John Kerry warned Russia it could face targeted sanctions including visa bans, asset freezes and trade isolation if it did not back down, and said major world powers were determined to isolate Moscow.
Moscow has said it is merely protecting the lives of Russian-speaking nationals, and appears to be calculating that the West will not risk a wider conflagration by taking anything approaching military action against it.
While Ukraine is associated to NATO, it is not a member and therefore cannot invoke the alliance's most powerful diplomatic tool, known as Article 5, which states that an attack against one member is an attack against all.