A House Republican lawmaker said Thursday that some members of the NATO alliance are still dependent on Russia for military equipment for their air and ground forces, which is makes it harder for the U.S. to count on them as allies.

"We have not weaned them off," Rep. Paul Cook, a retired Marine Corps colonel, said of those countries during a House Foreign Affairs subcommittee hearing.

The California Republican said the use of "Soviet-style" equipment is a complicating factor for U.S. policy. It leaves the eastern European NATO allies vulnerable to Russian aggression, in addition to complicating their efforts to fulfill President Trump's demand that they increase military spending.

"They still have to go back to the new Russia for those things that they have [had] for years and until they become a total member of NATO in terms of our military equipment and everything else, I think it diminishes their capability as a true ally," Cook told Pentagon and State Department officials during the hearing.

Cook urged the Trump administration to sell eastern European allies American military equipment that can replace the Russian weapons systems. "It doesn't seem like a big priority, and yet, countries there, they've been with us and everything else, but we expect them to come to the fight when and if the Russians come across," he said.

The allies have to want to make such deals, though. "I am seeing on my travels a desire to move away from Russian equipment and into NATO standard type equipment," Vice Admiral Joseph Rixey, director of the U.S. Defense Security Cooperation Agency, told Cook. "We are prepared to execute if requested."

The prevalence of Russian military equipment among some U.S. allies also hampered efforts to impose new sanctions again Russia in response to its aggression in Syria and Ukraine, and cyberattacks against the Democratic party in 2016.

"We're looking long and hard about allies that have Russian equipment," Sen. Lindsey Graham, R-S.C., told the Washington Examiner about a new Russia sanctions bill that passed the Senate today. "I think they negotiated a pretty good compromise ... what we're trying to do is make sure we don't undermine our allies but also go after [Russian President Vladimir] Putin."