NATO's top official accused Moscow outright on Thursday of attacking Ukraine as allied leaders gathered for a summit to buttress support for Kiev and bolster defenses against a Russia they now see as hostile for the first time since the Cold War.

U.S. President Barack Obama and his 27 allies meeting at a golf resort in Wales will also discuss how to tackle the Islamic State straddling parts of Iraq and Syria, which has emerged as a new threat on the alliance's southern flank, and how to stabilize Afghanistan when NATO forces leave at year's end.

"We are faced with a dramatically changed security environment," NATO Secretary-General Anders Fogh Rasmussen told reporters on arrival at the summit. "To the east, Russia is attacking Ukraine."

His statement stepped up Western rhetoric against Moscow and set the tone for a two-day meeting marked by a return to east-west confrontation 25 years after the fall of the Berlin Wall.

Reuters