Russia's likely conducting banned nuclear tests, U.S. official says

Details: Ashley said Russia was likely testing weapons in the Novaya Zemlya islands, an archipelago in the Arctic Ocean in northern Russia. He believes it intends to increase its nuclear arsenal "significantly" over the next decade.

Why it matters: This is the first time the U.S. has suggested Russia might have effectively violated its commitments under the 1996 Comprehensive Nuclear Test Ban Treaty.

• It's a critical time for U.S.-Russian relations. The Trump administration announced in February it would withdraw from the Cold-War era Intermediate-Range Nuclear Forces Treaty, due to formally end in August. The Pentagon plans to then begin testing missiles banned under the treaty.

The big picture: Russia has said it complies with the treaty, which it ratified in 2008. The U.S. has signed the treaty but not ratified it.

What they're saying: The Comprehensive Nuclear Test Ban Treaty Organization, which bans nuclear weapons testing, said in a statement it hadn't detected any unusual activity, per the BBC.

Go deeper: How Russia's old threat became new again