US Secretary of State Mike Pompeo said Tuesday he warned Russian Foreign Minister Sergei Lavrov of reprisals if Moscow interferes in next year's presidential election.

"On the question of interference in our domestic affairs I was clear, it's unacceptable," Pompeo told a joint news conference with Lavrov in Washington.

"Should Russia or a foreign actor take steps to undermine our democratic processes, we will take action in response," he said.

Lavrov again dismissed US intelligence's findings that Russia interfered in the 2016 election to back Trump.

"We have highlighted once again that all speculations about our alleged interference in domestic processes in the United States are baseless," Lavrov said.

Lavrov renewed an offer by Russia - which has been angered by US support for non-governmental organizations - for the two nations to sign an agreement on non-interference in each other's affairs.