American top diplomat Marco Rubio said late Wednesday that the U.S. is running out of options to sanction Russia after hammering the Kremlin’s biggest oil giants last month.

“Well, there’s not a lot left to sanction from our part, I mean, we hit their major oil companies, which is what everybody’s been asking for,” Rubio said before a meeting of G7 foreign ministers.

Last month, the U.S. slapped sanctions on Rosneft and Lukoil and their subsidiaries, in a bid to reduce Russia’s oil revenues — its main financing source for the war on Ukraine — and push Moscow to the negotiating table in a bid to end the Kremlin’s aggression.

Sanctions come into full force on Nov. 21, but several countries are already thinking about asking for exemptions. Hungary already got a one-year extension from the U.S.

“Sanctions have to be enforced, so you know we don’t put sanctions and then not enforce them. We’re interested in enforcing them as well,” Rubio added.

The sanctions’ success ultimately depends on the enforcement progress. One of the enforcement mechanisms is sanctioning the Russian shadow fleet — hundreds of oil tankers illegally transporting sanctioned Russian oil around the world.

“Shadow fleet has come up because I do think there are things that the Europeans can do on shadow fleet since a lot of these are happening in areas much closer to them,” Rubio said.

The EU has leveled 19 packages of sanctions against Russia, hitting Russia’s LNG, banks, crypto trading, further clamping down on the shadow fleet that clandestinely moves sanctioned goods, and more, aiming to reduce the Russian war economy.

The Ukrainian government said it knows there’s more to sanction and is ready to work with partners to show them.

“Regarding Rubio’s statement about exhausting sanctions options … there are absolutely more objective options out there. More oil majors, banks, and  fleet/infrastructure. And components and defense. And payments. And the Arctic,” said Vladyslav Vlasiuk, Ukrainian President Volodymyr Zelenskyy’s sanctions envoy.

“We continue to work with American partners, and with the G7, and with others. There will be more sanctions,” Vlasiuk added.