The bipartisan committee, which is nearing the end of its investigation, has found no proof that US President Donald Trump formed a corrupt pact with Russia to offer sanctions relief or other favorable treatment in return for Russian help during the election, NBC News reported citing Democrats and Republics on the committee.
According to the report, Trump and his associates had more than 100 contacts with Russians before the January 2017 presidential inauguration.
Democratic Senate investigators told NBC News that it may take them six or seven months to write their final report.
The US president has dismissed Mueller's probe a political witch hunt that has not produced any evidence in two years.
Russia has repeatedly denied interfering in the US election, saying the allegations were made up to excuse the defeat of Trump's campaign opponent as well as deflect public attention from actual instances of electoral fraud and corruption.