Speaking of Russia's 2,000 peacekeeping troops in the South Caucasus conflict zone, Devigne said: "Did any of these peacekeepers do anything? Nothing. They didn't even put their armoured vehicles in the road … passively to block the military operation," he said.

"There's only Russian troops [there]. Who is to be blamed? Russia," he added.

He spoke one day after Azerbaijan rolled through the Russian lines to force the surrender of the ethnic Armenian exclave of Nagorno-Karabakh.

Civilian EU monitors on the Armenian side of the border heard "numerous explosions, 15 here, five there … it was a military operation of an important scale," Devigne said.

And one "cynical" reason for Russia's green light was that a humiliating defeat by Azerbaijan for Armenian prime minister Nikol Pashinyan could see him fall from power to be replaced by a pro-Russian figure, the EU official said.

The war could also push up to 200,000 refugees from Nagorno-Karabakh into Armenia, a country of just 2.8 million people, placing a huge burden on Pashinyan's government.

Devigne highlighted a tweet by former Russian leader Dmitry Medvedev, who said the Azeri attack showed what happened if you "flirt with Nato", referring to a recent small-scale Armenia-US military exercise.

"I know from some experience how the Russians hate that, so I think this is a factor," Devigne said.

"[Russian president Vladimir] Putin never accepted that Pashinyan rose to power the way he did, in what you might call a Colour Revolution," Devigne also said, referring to the Armenian revolution in 2018 and to other non-violent regime changes in the former Soviet region.

Several MEPs called for sanctions against Azerbaijan and accused it of seeking "ethnic cleansing" of Armenians from conquered lands.

"We should get rid of this [EU] need to get gas from there [Azerbaijan] — that would weaken their stance," said German centre-right MEP Michael Mahler.

And not a single EU deputy had a good word to say about Baku, even though Azerbaijan had been bending over backwards to make friends in the EU parliament in recent times.

The EU bought 11.3 billion cubic meters (bcm) of gas from Azerbaijan last year — a jump from 8 bcm the year before, but still just 3 percent of its total annual imports.

EU ambassadors also held behind-closed-doors talks in Brussels on Wednesday which likely discussed potential sanctions, Devigne said.

But there was no consensus for sanctions in earlier talks in August, Devigne added, when Azerbaijan was already blockading Nagorno-Karabakh in preparation for its onslaught.

For his part, Devigne's boss, EU foreign affairs chief Josep Borrell, also met the Armenian foreign minister in the margins of the UN General Assembly in New York on Wednesday to voice solidarity.

France called a meeting of the UN Security Council amid uncertainty if an Azeri-Armenian ceasefire agreed on Wednesday will hold.

Azerbaijan's Nagorno-Karabakh campaign began with a first attack in 2020 and a second one in 2021.

It has been stockpiling Israeli and Turkish weapons and pumping out ever more belligerent anti-Armenian propaganda.

And it has belittled Europe, with its EU ambassador tweeting death threats against MEPs and its armed forces opening fire in the vicinity of EU monitors in Armenia earlier this year.

But if Russia facilitated the latest warfare and previous attacks, the EU also did little to put pressure on Baku in the build-up to the new hostilities, with European Commission president Ursula von der Leyen instead going there last summer to shake hands on gas deals with Azerbaijan's president, Ilham Aliyev, who she called a "trusted partner".

Asked by press in Brussels on Wednesday if von der Leyen now regretted cozying up to Aliyev, her spokeswoman declined to answer.

"It's a fact Azerbaijan is a supplier of gas to the EU. There's cooperation on energy, which is very sectoral, and reflects the need to diversify supply," the commission said.

Meanwhile, French liberal MEP Nathalie Loiseau gave an idea of how top EU diplomats ought to be feeling.

She had watched the events unfold with a "mixture of sadness, anger, and shame", she told Devigne in the EU parliament hearing.

"For months, Azerbaijan has been circling, starving, and bringing Armenians in Nagorno-Karabakh to their knees. Now it bombs Stepanakert [the Nagorno-Karabakh capital]. What have we done? Mediation? Total failure," she said.

"We ignored all the signs from the Armenian prime minister, who was telling us that Russia had abandoned Armenia. He called for help," she added.

"We just closed our eyes to this," she said.