Zuckerberg: Facebook is in 'arms race' with Russia

Facebook CEO Mark Zuckerberg has told US senators his company is in a constant battle with Russian operators seeking to exploit the social network.

"This is an arms race. They're going to keep getting better," he said.

Mr Zuckerberg was answering questions in the wake of the Cambridge Analytica data collection scandal.

He also revealed Robert Mueller, the special counsel investigating alleged Russian meddling in the 2016 election, had interviewed Facebook staff.

Mr Zuckerberg said he has not been among those interviewed by Mr Mueller's office.

But he added: "Our work with the special counsel is confidential and I want to make sure that in an open session I'm not revealing something that's confidential."