President Donald Trump, with Defense Secretary James Mattis, speaks during a Cabinet meeting in the Cabinet Room of the White House on March 8, 2018 in Washington, DC.

WASHINGTON — The Pentagon said Monday that Defense Secretary James Mattis is "completely aligned" with President Donald Trump's seemingly abrupt announcement to pull the U.S. out of an arms control treaty with Russia.

"The secretary of Defense has consistently said that Russia has not been in compliance with the treaty," Pentagon spokesman Col. Rob Manning said. "The secretary is completely aligned with the president, and he is in close contact with the president on this."

Earlier this month, Mattis told reporters in Brussels that any decision to withdraw from the Intermediate-Range Nuclear Forces, or INF, treaty would be done in consultation with NATO partners since Russian missiles pose an immediate threat to allies in the region.

"This will be a decision obviously made in concert with our allies by the president," Mattis said at the time. "We are trying to bring them [Russia] still back into compliance. And now is the time. It's gone on long enough."

When asked whether Mattis coordinated with NATO counterparts in the wake of Trump's announcement, the Pentagon directed the query to the White House. The White House has yet to respond to CNBC's request for comment.

Over the weekend, Trump said it was "unacceptable" for the U.S. to continue to adhere to the Intermediate-Range Nuclear Forces Treaty while Russia and China pursue nuclear weapons.

The 1987 treaty, signed by Russia and the U.S., prohibits the production or testing of ground-launched cruise missiles with a range of approximately 300 to 3,400 miles.