(Army National Guard photo by Sgt. 1st Class Jim Greenhill)

The U.S. defense secretary has again accused Russia of violating a key Cold War arms control treaty, calling the unresolved and increasingly tense dispute with Moscow "untenable."

Jim Mattis's remarks on Oct. 4, 2018 after a meeting of NATO military leaders were the latest in a series of increasingly blunt statements by U.S. officials regarding the 1987 Intermediate-Range Nuclear Forces treaty.

Russia has repeatedly denied U.S. assertions, first made publicly in 2014, that a ground-launched cruise missile Moscow has developed, and reportedly deployed, is in violation of the agreement, known as the INF treaty.


After years of public criticism of Moscow, U.S. officials in 2017 started becoming more aggressive in their approach. And Russia acknowledged the existence of a missile identified by Washington, but denied that it had violated the treaty.

In early October 2018, the U.S. ambassador to NATO, Kay Bailey Hutchison, said U.S. forces might have to "take out" the Russian missiles if the dispute continues. She later clarified that she wasn't referring to an actual U.S. military attack.

Defense Secretary James N. Mattis speaks with NATO Secretary General Jens Stoltenberg and Ambassador Kay Bailey Hutchison, the U.S. Ambassador to NATO at NATO headquarters in Brussels, Feb. 14, 2018.

(NATO photo)

"Russia must return to compliance with the INF treaty or the U.S. will need to respond to its cavalier disregard for the treaty's specific limits," Mattis said in Brussels.

"The current situation with Russia in blatant violation of this treaty is untenable," he said.

Congress has backed funding for a new missile program to counter the Russian weapon, and Mattis said in early 2018 that defense planners were working on new low-yield nuclear weapons to force Russia back into compliance.

NATO Secretary-General Jens Stoltenberg echoed Mattis's comments, saying Russia was imperiling the treaty, which is widely considered a "cornerstone" of European security.

This article originally appeared on Radio Free Europe/Radio Liberty. Follow @RFERL on Twitter.