The investigation focuses on the activities of Mr Trump's former campaign manager Paul Manafort, businessman and foreign policy adviser Carter Page and Republican political consultant Roger Stone, according to The New York Times.
The agencies involved in the inquiry are the Federal Bureau of Investigation, the CIA, the National Security Agency, the Justice Department, the Treasury Department's Financial Crimes Enforcement Network and representatives of the director of national intelligence, the sources said.
Officials say the working group began operating last spring, and that investigators are still trying to figure out how the Russian government would've moved all the money necessary to "covertly help Trump win", theorizing that they were using a system for Russian pensioners living in the US.
If that report (initially from the BBC) is accurate, it might suggest the anti-Trump investigation was initiated by one of the Baltic states, during a time in the primary season in which Trump was being attacked for criticism of the amount of money the USA spends on North Atlantic Treaty Organisation, a sore spot for the Baltic states.
According to the report, Manafort - who resigned as national chairman of Trump's presidential campaign in August 2016 - had business dealings in Russian Federation and Ukraine.
Michelle Obama's face was'like thunder during the ceremony
Manafort, in a response to the Times, said he had no contact with Russian officials and had not directed any others to have such contact. This report seemed to confirm previous indications that the United States government has collected sensitive intelligence about interactions between Trump insiders and Russians.
Reacting to the allegations, Manafort said in an emailed statement, "I have never had any relationship with the Russian government or any Russian officials".
"The investigators have accelerated their efforts in recent weeks but have found no conclusive evidence of wrongdoing, the officials said".
All Americans should agree that Russian interference in our nation's democratic processes is a matter of grave national importance. An official told the NYT that intelligence reports based on wiretapped communications were provided to the White House. It is unclear if the intercepts being examined have any connection to the Trump campaign. Manafort called the allegations of his ties to Russian Federation a "Democrat Party dirty trick and completely false".
"We have absolutely no knowledge of any investigation or even a basis for such an investigation", said Trump spokeswoman Hope Hicks.