* NATO says satellite pictures show Russian troops on border
* Moscow says photos out of date, NATO just rallying members
* Lavrov: NATO forces in E. Europe would violate agreements (Combines stories from Moscow and Prague, adds NATO satellite pictures, Lavrov)
By Gabriela Baczynska and Jason Hovet
MOSCOW/PRAGUE, April 10 (Reuters) - Russia accused NATO on Thursday of using the Ukraine crisis to justify its existence by creating an imaginary threat, while the alliance's head urged Moscow to pull its troops back from the Ukrainian border.
NATO published satellite pictures it said showed Russia's military buildup, but Moscow immediately dismissed them, saying they were from last August.
NATO Secretary General Anders Fogh Rasmussen, who accuses Moscow of amassing 40,000 combat-ready troops near Ukraine's border, said: "We have seen the satellite images day after day.
"Russia is stirring up ethnic tensions in eastern Ukraine and provoking unrest. And Russia is using its military might to dictate that Ukraine should become a federal, neutral state. That is a decision which only Ukraine as a sovereign state can make," Rasmussen told a news conference in Prague.
Moscow dismissed the Western concerns as "groundless". It said Rasmussen was being confrontational and not offering "any constructive agenda" for Ukraine.
"The constant accusations against us by the secretary general convince us that the alliance is trying to use the crisis in Ukraine to rally its ranks in the face of an imaginary external threat to NATO members and to strengthen demand for the alliance ... in the 21st century," the Russian Foreign Ministry said in a statement.
Moscow has proposed that Ukraine's neutrality should be enshrined in law, meaning it would not be able to join NATO or the European Union, a motion unacceptable for the new pro-Western authorities in Kiev.
NATO and the West accuse Russia of stirring unrest in eastern parts of the country, where Moscow says it has the right to protect Russian-speakers from the new authorities in Kiev it deems illegitimate.
Rasmussen reiterated his call on Moscow to pull back its troops.
"I have this message to Russia: You have a choice to stop blaming others for your own actions, to stop massing your troops, to stop escalating this crisis and start engaging in a genuine dialogue," he said.
"If Russia is serious about a dialogue, the first step should be to pull back its troops."
NATO has responded to the crisis by promising an increased presence in its central and eastern European members - firmly in Moscow's orbit until the 1991 Soviet Union collapse - including in Ukraine's neighbour Poland.
Russian Foreign Minister Sergei Lavrov said deployment of NATO forces in eastern European countries close to Russia would violate the 1997 Founding Act, a cooperation agreement between Moscow and the alliance.
"The fact that now, under the pressure (of eastern NATO members) NATO is forced to consider deploying troops and installations on territories closely adjacent to Russia, this is a violation of the Founding Act," Lavrov said. (Additional reporting by Steve Gutterman and Adrian Croft; Writing by Gabriela Baczynska; Editing by Robin Pomeroy)