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PARIS, April 8 (Reuters) - NATO's secretary-general warned Russia on Tuesday that if it were to encroach into eastern Ukraine there would be "grave consequences" for its relationship with the alliance.
Police detained 70 people occupying a regional administration building in eastern Ukraine overnight, but pro-Moscow protesters held out in a standoff in two other cities in what Kiev called a Russian-led plan to dismember the country.
Kiev says the seizure of public buildings in eastern Ukraine's mainly Russian-speaking industrial heartland on Sunday night is a replay of events in Crimea, the Black Sea peninsula Moscow annexed last month.
"If Russia were to intervene further in Ukraine it would be a historic mistake," Anders Fogh Rasmussen told a news conference in Paris. "It would have grave consequences for our relationship with Russia and would further isolate Russia internationally."
Rasmussen said it was premature to talk about a military response were Russia to move into eastern Ukraine, but urged Moscow to pull back the "tens of thousands of troops" that had massed on Ukraine's borders.
"We have all plans in place to ensure effective defence and protection of our allies," he said. "It is obvious that the evolving security situation in Ukraine and along its borders make it necessary to review our defence plans and look at how we could strengthen our collective defence."
He said NATO was reviewing a 1997 co-operation agreement with Russia and subsequent Rome declaration of 2002 that prevented NATO setting up bases in eastern and central Europe and its foreign ministers would decide on that in June.
"Those decisions will be impacted by the situation in Ukraine and Russian behaviour," Rasmussen said.
When asked whether France should cancel a deal to sell two helicopter carriers before the first one is delivered later this year, Rasmussen said:
"I am not going to interfere with national decisions, but I am confident that France will take the necessary decisions taking into account all the concerns that have been expressed." (Reporting By John Irish; Editing by Nick Vinocur and Mark John, Ralph Boulton)