David Petraeus, a retired US general and former head of the CIA, told CNN he believes Ukrainian forces could push Russian forces further this summer, depending on arms shipments and strategy.

To push back the Russians, the Ukrainians will need an all-out war — a complementary approach in which multiple types of combat units support each other — Petraeus told CNN’s Nick Robertson at a security conference in Munich, Germany.

“You can make the enemy break and ideally collapse — and that’s possible this summer, at least locally — and hopefully enough to cut that land bridge that Russia has put up that allows them to link up with Crimea along the southeast the coast of Ukraine,” said Petraeus, who served as a U.S. and coalition commander in the wars in Afghanistan and Iraq and later served as director of the CIA.

“If you cut it off, you can start isolating Crimea, (…) and then you can divide the Russian forces. And then, if you can knock out the Kerch bridge, you really isolated them,” he added.

Petraeus said that if this scenario were to come to fruition, combined with long-range weapons for highly mobile artillery rocket systems (HIMARS), there would be a “very different dynamic” in the conflict.

If Russian casualties continue to pile up, “at some point the Kremlin will have to admit that this war is unsustainable on the battlefield,” and not just by tightening economic and financial controls.

He also said that Ukrainians who train with Western weapons seem to learn at an extraordinary speed.

Petraeus also noted that, according to reports from colleagues who train Ukrainian soldiers, they “go wild” in training, and when they return to the barracks after a full day of training, they continue to read textbooks because “they want to go back to the fight to protect their families “.

Ukrainian troops are training with Leopard 2 tanks in Poland, the British government said earlier this month it would begin training Ukrainian pilots on NATO-standard fighter jets, and the first group of Ukrainians completed training at a US base in Germany on Friday.

“I think they will be able to achieve a common weapons effect that the Russians haven’t,” Petraeus said.