The top US general told CNN on Monday that while Ukraine is "very well prepared" for a counteroffensive against Russia, it is "too early to tell what outcomes are going to happen."

"They're in a war that's an existential threat for the very survival of Ukraine and has greater meaning for the rest of the world — for Europe, really for the United States, but also for the globe," Chairman of the Joint Chiefs of Staff Mark Milley said in an exclusive interview with Oren Liebermann from Normandy, France.

Milley, who is retiring this year, is in Normandy to commemorate the 79th anniversary of the 1944 D-Day invasion — a massive World War II operation that he called the "greatest amphibious invasion in human history" — as the war continues to rage in Ukraine.

For months now, the US and its allies have been helping arm Ukraine for the counteroffensive, which was expected to start in the spring. Most recently, the US said it would support a joint effort by other nations to train Ukrainian pilots on F-16 fighter jets.

Russia has already begun to claim that it has repelled a "large scale offensive," in southern Donetsk, though they have not provided evidence to support the claim.

The war has also begun creeping into Russia, as suspected Ukrainian drone strikes hit inside Moscow and a shelling attack was carried out in Belgorod. Asked Monday if such attacks would risk escalating the conflict, Milley said there is "always risk" of escalation, and it's something the US is watching "very, very carefully."

This story is breaking and will be updated.