Russian oil tycoon-turned-dissident Mikhail Khodorkovsky on Tuesday accused the EU of committing a massive blunder with oil sanctions against Moscow that are now undermining the 27-nation bloc economically rather than depleting the Kremlin's war chest.

Russia's former richest man said the EU should have secured alternative supplies before moving ahead with an embargo, or should have considered another approach entirely such as slapping tariffs on Russian energy rather than imposing an outright ban. By drilling a hole in its own finances, Khodorkovsky argued that Europe was now less able to pour cash into the all-important task of buying more weapons for Ukraine.

After one month of negotiations, EU member countries agreed to ban seaborne shipments of oil from Russia by the end of this year — equivalent to over 90 percent of imports — in late May.

“At the moment, energy sanctions are hurting Europe, not Russia," he said, speaking to POLITICO during his first trip to the EU since the war in Ukraine began. "My point of view was and remains the same — what on earth are you doing?"

Khodorkovsky, the former head of oil giant Yukos, spent 10 years in prison on what were widely seen as trumped-up charges after he became an outspoken critic of the Kremlin. Following his release in 2013, Khodorkovsky has campaigned to promote democracy and human rights in Russia through his Open Russia organization.

“The problem is that current Western politicians have never held talks with a gangster,” he said, referring to Russian President Vladimir Putin. “You can only start negotiating with him when he feels like he's in a weaker position."

Khodorkovsky, in Brussels for two days of meetings with EU officials and others organized by the Bratislava-based think tank GLOBSEC, argues the bloc could have better spent its cash on arms for Ukraine.

“How much has the West lost in revenue by introducing all kinds of energy sanctions? $100 billion, $200 billion?" he said. “Had Ukraine got at least $50 billion worth of weapons instead of $10 billion, the situation would be completely different now — without any energy sanctions being introduced.”

The EU marked down its growth predictions for this year by around 1 percent in April amid the war in Ukraine — equivalent to around €160 billion, based on recent GDP estimates from the International Monetary Fund. Meanwhile, the bloc is putting €2 billion toward arms for Ukraine.

In line with Khodorkovsky's thinking, several experts have argued that imposing tariffs would have been smart since redirecting oil to other countries with the infrastructure currently in place would have been difficult for Moscow. This means Russian energy companies would likely have absorbed the higher export costs to Europe, reducing their margins and ultimately cutting into Moscow's military budget.

Finally, the former billionaire said Europe should have made more concerted efforts to find alternative supplies for its oil and gas well before imposing sanctions. Instead, EU countries have had to replace Russian energy supplies by hurriedly negotiating ad hoc contracts.

“I was amazed when I discovered that there had been no agreement on any alternative supplies and then and [now] you're introducing sanctions?” Khodorkovsky said.