As U.S. President Donald Trump and Russian President Vladimir Putin met Friday at the G-20 Summit in Hamburg, Germany, there was a different meeting happening some 4,000 miles away in Washington.

At the Pentagon, U.S. Defense Secretary James Mattis and U.K. Defense Secretary Michael Fallon talked about ways NATO could improve its combat power and deter Russia aggression in Eastern Europe.

"We...reviewed this morning Russian aggression, where we alongside the United States are providing essential reassurance on the eastern flank of NATO to our Eastern European allies," Fallon told a small group of American reporters Friday after his meeting with Mattis.

The meetings show that even as the White House seeks to improve relations with Moscow, U.S. and UK defense leaders still view Russia as a severe military threat.

Fallon, meeting with Mattis for the sixth time this year, cited a January speech by U.K. Prime Minister Theresa May, who told U.S. lawmakers in Philadelphia to “engage but beware” of Russia.

“It’s important that the two presidents understand each other clearly,” Fallon said Friday. “NATO should be transparent and open about its deployments. It’s also important to talk to Russia about those areas of the world where Russia has great influence, particularly over the Syrian regime where Russia could have ended this civil war much earlier if it had chosen to do so.”

Fallon also noted that Russian troops still occupy eastern Ukraine.

“We don’t think it can be business as usual between the West and Putin until the Minsk agreements are properly respected and until we see the territorial integrity and sovereignty of Ukraine restored,” he said. “This can’t be business as usual, but we welcome the dialogue that’s taking place.”

The U.K. defense secretary touted the British troops deployed to Estonia and Poland alongside American forces. Fallon also boasted about Royal Air Force Typhoon fighters operating from Romania to police the skies over the Black Sea.

"Whatever the future holds, we agree that NATO has to remain our bedrock," Fallon said.

The U.K. secretary said London still plans to boost defense spending even though the British pound has fallen in value since last year’s vote to leave the European Union.

“Like any large organization, we take precautions against movements in the currency,” he said. “It’s too early at the moment to say where that rate will eventually settle down.”

He said the weaker pound is not affecting UK arms purchases at the moment.

Fallon said Trump "was right to say that alliance members must spend more," he said. "We and the United States are doing our bit."

Fallon said others across the alliance are also working to "up their game, cumulatively increasing spending across Europe and Canada by some $46 billion."

The defense leaders also talked about ways to make the alliance more agile and adaptable to “produce a coherent force that is capable of meaningful action to tackle international terror from all directions."