US Defence Secretary Ash Carter says the United States’ response so far to Russia orchestrating hacks during the 2016 presidential campaign is just the start.

“Some responses have been made. I think you should regard that as a start and not the end,” Carter said during a news briefing at the Pentagon alongside the chairman of the Joint Chiefs of Staff, Marine General Joseph Dunford.

Last month, President Barack Obama ordered the expulsion of 35 Russian suspected spies and imposed sanctions on two intelligence agencies over their involvement in hacking US political groups in the 2016 presidential election.

The Kremlin has said the US hacking allegations are “reminiscent of a witch-hunt.”

US intelligence agencies on Friday released an assessment that Russian President Vladimir Putin ordered a covert effort to help Republican Trump’s electoral chances by discrediting Clinton.

The report, which omitted classified details, was the US government’s starkest public description of what it says was a Russian effort to manipulate the American electoral process by leaking hacked emails from Democrats.

Russia has denied interfering in the election but President Barack Obama expelled 35 Russian suspected spies from the US and imposed sanctions on two Russian intelligence agencies last month in response to the allegations.

“We did not develop any evidence that the Trump campaign, or the current RNC, was successfully hacked,” Comey told lawmakers. He did not say whether Russia had tried to hack Trump’s campaign.

Trump has disputed the accusations of Russian cyber attacks during the election but his incoming chief of staff said on Sunday that the New York businessman accepts the US intelligence community’s conclusion that Russia engaged in hacking during the campaign and may take action in response.

Comey declined to comment on whether or not the FBI might be investigating links between Russia and associates of Trump, who frequently called during the campaign for improved relations between Washington and Moscow.

The FBI director was pressed by Senator Ron Wyden, an Oregon Democrat, to publicly provide a declassified answer to the question before January 20, the day Trump will be inaugurated, but Comey suggested he would unable to do so.