The US Department of State confirmed on Thursday that Ambassador Sullivan intends to return to Moscow, Russia, in the coming weeks.
"Ambassador Sullivan has been deeply engaged in the preparations for the upcoming meeting between President [Joe] Biden and [Russian] President [Vladimir] Putin," State Department spokesperson Ned Price said. "We have [an] expectation that he will return to Moscow in the coming weeks."
No concrete date was provided for Sullivan's trip. Putin and Biden are slated to meet on June 16, at the Villa La Grange in Geneva, Switzerland.
Sullivan has remained in the US since late April, after it was recommended that he leave Russia and return to Washington for consultations.
The ambassador's return to the US came amid the tit-for-tat expulsion of ambassadors in both the US and Russia.
"It is obvious that the extremely tense situation currently implies an objective need for the ambassadors of both our countries to be in their capitals to analyze the situation and hold consultations," the Russian Foreign Ministry said in a statement issued after the US expelled 10 Russian diplomats.
At the time, the US had also announced sweeping sanctions against 32 Russian entities and individuals, alleging that they were behind a series of cyber attacks in the US.
During his time back in the US, Sullivan has reportedly briefed members of Congress on diplomatic efforts with Russia.
According to sources that spoke with CNN, Sullivan testified to the Senate Foreign Relations Committee that Biden should tread lightly during his upcoming summit with Putin, as he believes the Russian president "has not really changed his stripes."
He also reportedly advocated for more in-person engagements between US and Russian officials, warning that actions such as sanctions were unlikely to work.
The State Department spokesperson has claimed that the reporting of Sullivan's testimony during a "classified hearing" is "wildly off base."
"As we engage Russia in ways that advance American interests, we remain clear eyed about the challenges that Russia poses and will work to hold Russia to account for its reckless and adversarial actions," Price said.