(CNN) Russia's military deployment in Syria to back Bashar al-Assad "is not a winning strategy," America's ambassador to the United Nations said Monday.

"Doubling down on a regime that gases its people, that barrel bombs its people, that tortures people who it arrests simply for protesting and for claiming their rights -- that's just not going to work," Samantha Power told CNN's Christiane Amanpour.

U.S. President Barack Obama said Friday that al-Assad "is worried enough that he is inviting Russian advisers in and Russian equipment," and Reuters reported Monday that Russia had begun deploying several tanks to a Syrian airfield.

"Even if you were Machiavelli and all you cared about was ISIL," Power said, using the U.S. government's preferred abbreviation for ISIS, "to support a regime like this and to not take account of the views of the vast majority of the Syrian people that want to go in a different direction is not going to either bring peace or actually succeed in defeating terrorism, which is what President Putin says his priority is."

The tens of thousands of refugees streaming across Europe's borders has put renewed focus on the war in Syria. At least 200,000 people have been killed in the more than four-year-long civil war -- activists put the number at more than 310,000.

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