Washington (CNN) The ability of the U.S. and Canadian military to defend North America could be jeopardized by stepped up Russian military activity, according to the commander of the North American Aerospace Defense Command.

Adm. William Gortney told the Senate Armed Services Committee on Thursday that Russia is continuing to work on its program to deploy "long-range conventionally armed cruise missiles," that can be launched from its bomber aircraft, submarines and warships. This is giving the Kremlin "deterrent" options "short of the nuclear threshold," Gortney said.

JUST WATCHED Is Russia arming up for a new Cold War? Replay More Videos ... MUST WATCH Is Russia arming up for a new Cold War? 01:56

"Should these trends continue over time, NORAD will face increased risk in our ability to defend North America against Russian air, maritime and cruise missile threats," he said.

Gortney's remarks came in written testimony submitted to the committee.