Censor.NET reports citing Reuters.
Speaking before the Congress on Thursday, Mattis said America must be ready to confront Moscow where necessary, even as he backed Trump's bid for better relations.
According to him, Russia, China and Islamist militants were presenting the biggest challenge to the U.S.-led world order since World War II.
Mattis said he wanted to meet with the new Trump national security team to "craft a strategy to confront Russia for what it's done," when questioned about the possibility of new U.S. sanctions.
Mattis cited Russian involvement in hacking and information warfare among the challenges posed by Moscow. Others include treaty violations, destabilizing activities abroad and "alarming messages from Moscow regarding the use of nuclear weapons."
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