Story highlights Lavrov said "we never heard not a single fact" about alleged Russian collusion in the 2016 US election

Lavrov, who met privately with Tillerson on two occasions this week, also bemoaned the state of US-Russian relations

(CNN) At a news conference Friday on the sidelines of the United Nations General Assembly, Russian Foreign Minister Sergey Lavrov once again hit back on claims his country meddled in the 2016 US election, saying his American counterpart failed to offer any proof of interference.

"In about a year of this chaos about the so-called interference of Russia into the elections, we never heard not a single fact," Lavrov told reporters in New York. "When I asked (US Secretary of State) Rex Tillerson, 'How can we confirm his words that the interference of Russia into American process is well-documented,' he said, 'I cannot show you anything because this is confidential information.'"

"You know, I cannot believe that," he added, suggesting that any evidence of Russian malfeasance, if it existed, would have leaked to the media in the course of congressional investigations or the investigation currently being led by special prosecutor Robert Mueller.

Lavrov's comments come as Mueller's investigation appears to be entering an important stage , with investigators requesting documents and emails from the White House, suggesting that parts of Mueller's investigation are focusing on President Donald Trump's own actions.

Lavrov, who met privately with Tillerson on two occasions this week, also bemoaned the state of US-Russian relations in his news conference, blaming "Russo-phobic hysteria" in the United States for the strain.