honor ukraine s friendship with russia now coming down. marcus moore in kyiv tonight. reporter: tonight, the u.s. responding to russia s warning that tensions with the west over ukraine could risk world war iii and nuclear con fliblgt. that kind of rhetoric is very dangerous and unhelpful. nobody wants to see a nuclear war happen. it s a war that, you know, all sides lose. reporter: u.s. defense secretary austin was in germany meeting with military officials from over 40 countries and vowed to move, quote, heaven and earth, to help arm ukraine. he thanked germany for changing long-standing policy and for the first time agreeing to send 50 anti-aircraft tanks to e ukr ukraine. and he expanded on the u.s. wanting to see russia weakened. we would like to make sure again, that they don t have the same type of capability to bully their neighbors. reporter: in moscow today, u.n. secretary general antonio guterres met with vladimir putin and said an