The Russian ambassador was cited as saying it would be good to organize a meeting between Russian Defence Minister Sergei Shoigu and USA counterpart James Mattis, adding that a group of US lawmakers are also planning to visit Russia. Putin also talked about the Syria deal during his news conference with Trump, although few took note. The next day, members of the group attacked counterprotesters, firing at least one shot from a pistol and brutally beating 20-year-old Deandre Harris in a parking garage, before a neo-Nazi named James Alex Fields drove his vehicle into a crowd of anti-racist demonstrators, killing a local paralegal named Heather Heyer and injuring 19 others.
Hours after Antonov spoke, the White House shot down the idea, saying the Trump administration "is not considering supporting" such a referendum.
Parts of the regions that are controlled by Russia-backed separatists - the rebel "people's republics" of Donetsk and Luhansk - held their own referendums in May 2014 and declared independence from Ukraine.
During a joint press conference with Putin after their meeting in Helsinki, Trump said he didn't see "any reason" why Russian Federation would meddle, adding that Putin was "extremely strong and powerful in his denial". Limited details have emerged, but Antonov said discussions included ways to cooperate on arms control and Iran's nuclear activities.
White House spokeswoman Sarah Sanders said in a Twitter post that Trump had directed national security adviser John Bolton to issue the invitation, even though USA lawmakers and top officials in Trump's administration have not been briefed on what Trump and Putin discussed in Monday's summit with only interpreters present. Such a meeting would be another step towards discussing and resolving problems between the two countries, he said.
Trump clarified his remarks at the White House on Tuesday, saying that he misspoke and accepts the intelligence community's conclusions.
In a sign of support for the Ukraine government, the Pentagon said Friday it would provide $200 million in additional training, equipment and advisory assistance to Ukraine's military.
Related: Trump: War Games In South Korea Cancelled.
The first footage of a live launch of the Avangard hypersonic missile, which Moscow says boasts "a glider manoeuvring warhead", was also aired along with a clip of the heavy Sarmat intercontinental ballistic missile.
Russia's ambassador to the USA says Vladimir Putin and Donald Trump should continue to have direct contact after their summit this week. "In the United States, in Russian Federation, or anywhere else", he said in a statement.
Both he and Mr Trump, who held their first summit in Helsinki on Monday, have spoken of the need to avoid an arms race, and Mr Putin has spoken of the urgent need to work to extend the new START strategic arms reduction treaty.
The White House is still trying to clean up post-summit Trump statements on Russian interference in the 2016 election.