U.S. National Security Advisor John Bolton says he warned his Russian counterpart not to interfere in the U.S. mid-term elections in November.
Bolton said he made it clear the United States is "prepared to take necessary steps to prevent it from happening."
He spoke at a news conference in Geneva, where met with Russian national security council director Nikolai Patrushev.
Bolton said the issue prevented the issuance of a joint statement at the conclusion of the meeting, the first high-level meeting since U.S. President Donald Trump and Russian counterpart Vladimir Putin held talks in Helsinki last month.
The U.S. has already imposed economic sanctions against Russia over it's interference in the 2016 U.S. presidential election.
The U.S. intelligence community concluded Russia meddled in the election, a finding Russia denies.
Patrushev told reporters he and Bolton agreed to re-open communication lines between U.S. and Russian foreign and defense ministries, according to Russia's RIA news agency.
Patrushev also said the two agreed on resuming contacts between the two countries' army chiefs-of-staff, and that he invited Bolton and other U.S. officials to Russia for more talks at an undetermined date.
The two men also discussed Iran. Bolton said the Trump administration's goal is to "put maximum pressure on the regime" with more extensive and effective sanctions. The Trump administration previously withdrew from a 2015 global agreement aimed at curbing Iran's nuclear program.
With respect to Iran's role in Syria, Bolton said "our objective is that all Iranian forces return to Iran" and said a "variety of ways" were discussed to achieve that goal.