"There's no doubt the [US-Russia] relationship has worsened. He [Russian President Vladimir Putin] tried again to muck around in our elections just last month, and we are seeing a continued effort along those lines," Mattis said, giving a speech at the Ronald Reagan Presidential Library in California.
The same day, the heads of the Department of Homeland Security, Department of Justice, the FBI and the Director of National Intelligence said in a joint statement that there was no indication that election infrastructure had been compromised ahead of the vote.
Washington has also accused Moscow of meddling in the 2016 US presidential election, allegations which Russian officials have repeatedly denied as unfounded and an attempt to fuel Russophobic hysteria. Russia maintains that it has never interfered in the political system of the United States or any other country.