The gas deal between the U.S. and EU is important, but won’t be able to make up the shortfall from Russia, former U.S. energy secretary Dan Brouillette said on Monday.

The U.S. said it will work with international partners to provide at least 15 billion cubic meters more liquefied natural gas (LNG) to Europe this year. In 2021, the European Union imported 155 billion cubic meters of natural gas from Russia, according to the International Energy Agency.

“Frankly, I’m not quite sure that everyone can make up that shortfall. That’s an enormous amount of gas,” he said.

However, the gas deal is “very important,” and private industry and governments will have to fill the gap if Europe is to reduce its reliance on Russian gas, said Brouillette.

He added that Germany should also build regas facilities to convert LNG from liquid into gas to support the shift away from Russian energy in the short run.

In the longer term, Europe has to tap various energy sources as it tries to reach its carbon emissions goals, said Brouillette.

“When you look at the history of energy, it’s always been in transition, but it’s always been a transition of less to more,” he said. That’s in contrast to substituting one form of energy generation, such as burning fossil fuels, for another form of energy, like wind or solar power.

“To maintain the economic growth that all of these countries want, that the United States wants, it will take more energy, not less,” he said. “That’s the transition that we should focus on.”

Doing so will give countries energy security as well as national security, he said.

— CNBC’s Sam Meredith contributed to this report.