'Mr. Putin isn't done in east Ukraine'

He said the US sees Russia “stocking … important supplies, ammunition, etc., to levels that would support operations".

He also described Ukraine separatists as “a force that has been trained, that is led by Russian leadership ... and is ready to do whatever mission is required of it”.

Later on Thursday, at a defence ministers’ meeting, Nato secretary general Jens Stoltenberg added: “There is still a risk of a return to heavy fighting”.

“Russia continues to support the separatists with training, weapons, and soldiers. And it has large numbers of forces stationed on its border with Ukraine”.

He said that, despite Minsk II, the Russian side has “heavy weapons” near the contact line and is denying access to international monitors.

He noted that Nato is funding Ukraine cyber defences, command and control structures, and logistics capabilities.

He said it’s also helping to counter Russian propaganda: “We are doing communications every day, when we are providing facts … to highlight what is really going on”.

The US defence secretary, Ash Carter, said: “America's support for Ukraine is ongoing and robust ... Right now, for example, 300 US paratroopers from the 173rd Airborne Brigade are in Yavoriv [in west Ukraine] training the Ukrainian National Guard”.

Referring to EU economic sanctions, he said “political and economic pressure is key to countering Russia's ongoing aggression”.

Referring to concerns Russia might escalate beyond Ukraine, he said Nato is almost done deploying a “Very High Readiness Joint Task Force” in the Baltic states, Poland, Bulgaria, and Romania.

He said the US has “pre-positioned … tanks, infantry-fighting vehicles, artillery, and associated equipment” in the region. “Two of the battalion sets are already in Europe and a third will be here shortly”.

Saakashvili

For his part, Mikheil Saakashvili, the former Georgian leader, at a separate event on Thursday, issued similar warnings.

Saakashvili, who was recently appointed governor of the Odessa region in south Ukraine, told EUobserver at a gathering of centre-right EU leaders in Brussels, that: “Summer is a very dangerous period”.

“That's usually when [Russian president] Putin likes to fight his wars and dirty campaigns”.

He said the same thing at Globsec, a security congress in Bratislava, last weekend.

Odessa has one of the most pro-Russian populations in the country.

It also stands between Russian forces in Ukraine and in Moldova, where Putin has thousands of troops, stationed in the breakaway Transniestria region, and where a pro-Russian government is poised to take power in Chisinau.

Saakashvili said Putin intends to foment unrest in Odessa, as a pretext to push west, cutting off Ukraine from the Black Sea, and joining up with Moldova to encircle the country.

“The region will be next to blow up if we don’t do something”, he said.

Aleksashenko

But Sergei Aleksashenko, a former Russian deputy finance minister, who now works for US think tanks, outlined a different scenario.

He said Putin is an “opportunist” who seized Crimea because it was a soft target amid political unrest in Kiev last February.

But he said “Novorossiya”, Putin’s claim to east and south Ukraine, is on hold as a project because the cost, in terms of Russian casualties and Russian public support, would be too high.

Aleksashenko indicated that Putin is waiting for the Ukrainian economy and Ukraine’s new government to collapse to provide a new opportunity.

But he said that if Nato stationed a small force on the contact line he wouldn’t dare to cross it.

“Please send paratroopers to east Ukraine, not a lot: 2,000 or 3,000”, he told Globsec.

“Ukraine should be a line for Europe. Nato should take responsibility to protect it under the Budapest memorandum”, he said, referring to a 1994 treaty guaranteeing UK and US protection in return for Ukraine’s unilateral nuclear disarmament.