U.S. Air Force General Philip Breedlove told an audience here at the German Marshall Fund Brussels Forum that Moscow continues to ramp up military and economic support to separatists in Eastern Ukraine.
That conclusion was based on evidence gathered by the North Atlantic Treaty Organization's joint intelligence unit in the U.K.
“We continue to see disturbing elements of air defense, command and control, resupply and equipment coming across a completely porous border,” he said.
Under the agreement reached last month in Minsk, Belarus, Russia is obligated to withdraw all troops and equipment from Ukraine and return control of the border to the Kiev government by the end of this year.
The Organization for Security and Cooperation in Europe is supposed to monitor Russian compliance.
Breedlove said the Russian moves made Western consideration of arming Ukraine more pressing.
He didn’t outright endorse sending lethal aid, but according to many reports, he has been making that case inside the Barack Obama administration.
“What we see is diplomatic tools being used, informational tools being used, military tools being used, economic tools being used against Ukraine," he said.
"We in the West should consider using all of our tools in reply. Could it be destabilizing? The answer is yes. Also, inaction could be destabilizing.”
Victoria Nuland, the U.S. assistant secretary of state for European affairs, told the forum on Friday that Obama has not yet made a decision on arming the Kiev government.
Nuland has made no secret of her support for the measure, but has encountered reluctance from senior White House staff members who don’t want to break ranks with European partners or give Russia an excuse to counter-escalate.
“We’ve seen, month on month, more lethal weaponry of a higher caliber … poured into Ukraine by the separatist Russian allies," Nuland said.
"The kinds of equipment that the Ukrainian forces are confronting are much more sophisticated than what they have. I think the number one thing is for Russia to stop sending arms over the border so that we can have real politics.”
The European Union's high representative for foreign affairs, Federica Mogherini, refused to say whether she thought Russia was adhering to the Minsk pact.
She said European leaders won’t make a judgment until July, when the next decision on EU sanctions is due, and that she was working to ease sanctions against Russia.
“We decided more than one year ago that … the only way of putting pressure on Russia was the economic one,” she said.
“I wish we could lift the sanctions soon, but it depends on the situation on the ground in Ukraine.”
Konstantin Kosachev, chairman of the Russian parliament's international affairs committee, denied that any Russian troops are in Ukraine.
“We are not sending troops into neighboring country. Mr. Breedlove believes we do. But we do not,” he said, evoking scoffs from the mostly European and American audience.
Breedlove and Nuland are fighting an uphill battle.
Obama has said arming Kiev would be seen as an escalation and would unsettle the situation on the ground.
Yet NATO's evidence shows that Russia is changing the status quo every day.
So it's not arming Kiev that makes keeping the balance between the two sides impossible, raising the chances of greater violence.
Zbigniew Brzezinski, the former national security advisor to President Jimmy Carter, was highly critical of the West's approach.
“We have signaled a willingness to accommodate," he said.
"I’m not sure that, at this stage, we have succeeded in convincing the Russians that we are prepared to deter the kind of steps they are adopting.”
If Obama doesn’t want to give arms to Ukraine's military, he will have to find another way to turn up the heat on Putin.
Some in Congress, along with State Department and White House officials, are preparing new sanctions measures.
Yet while the White House waits for Europe to agree to either option, we get paralysis that plays into Putin’s hands.