Video: US-Russia diplomatic showdown

>>> good evening, our lead story tonight sounds like a throw-back to the height of the cold war era . tonight the united states and russia are at odds over what is now being called a civil war in syria . u.s. secretary of state hillary clinton is calling out russia publicly for sending attack helicopters to syria , just like the habits they have been using to crush the rebellion and kill civilians from above. it's been going on 15 months. it's brutal. it's estimated as many as 14,000 people have been killed and there are real questions about how this ends. our chief correspondent andrea mitchell in the d.c. newsroom starts us off tonight. andrea, good evening.

>> reporter: good evening. that ballots in syria is fought in a diplomatic showdown between the united states and russia . it does feel like a return to the cold war , only days before president obama is having his first summit with president putin . the blood shed is unrelenting. the u.n. now calls it a civil war . even u.n. monitors are under attack. massacres by civilians by government tanks and artillery and government-backed thugs. reports of children tortured and used as human shields . now a war of worlds between u.s. and russia , the supplier. secretary of state accusing them of contributing to the violence by sending the assad machine attack helicopters .

>> they continue to deliver. we believe that the situation is spiraling towards civil war . it's now time for everyone in the international community , including russia and all security councilmembers to sfoe assad with a unified voice and insist that the violence stop.

>> reporter: russia 's foreign minister denied it and said the u.s. was arming rebels, a charge that was immediately shot down.

>> i would emphasize the united states has provided no military support to the syrian opposition, none.

>> reporter: all this comes just days before a critical meeting between president obama and president putin of russia and a summit in mexico next week.

>> we are not going to accept russia continuing to send arms to syria . there will be grave consequences to our relationship if they continue that.

>> today france called for a no-fly zone over syria . the strategy nato used to topple gadhafi. secretary of state colin powell argued the u.s. should not get in the middle of syria 's civil war .

>> if you take out this government as we learned in afghanistan and iraq, you now become responsible for the country. i don't think that should be our responsibility.

>> brian, late today russia backed off of the charge that the u.s. was arming the syrian rebels saying its foreign minister was somehow mistranslated. those russian helicopters remain a contentious issue and a potential game changer with government assad in the continuing efforts to crush the opposition.

>> andrea mitchell starting us off from the washington bureau. andrea,

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