American law enforcement and intelligence agencies are examining intercepted communications and financial transactions as part of a broad investigation into possible links between Russian officials and associates of President-elect Donald J. Trump, including his former campaign chairman Paul Manafort, current and former senior American officials said.
The continuing counterintelligence investigation means that Mr. Trump will take the oath of office on Friday with his associates under investigation and after the intelligence agencies concluded that the Russian government had worked to help elect him. As president, Mr. Trump will oversee those agencies and have the authority to redirect or stop at least some of these efforts.
The counterintelligence investigation centers at least in part on the business dealings that some of the president-elect’s past and present advisers have had with Russia. Mr. Manafort has done business in Ukraine and Russia. Some of his contacts there were under surveillance by the National Security Agency for suspected links to Russia’s Federal Security Service, one of the officials said.
Mr. Manafort is among at least three Trump campaign advisers whose possible links to Russia are under scrutiny. Two others are Carter Page, a businessman and former foreign policy adviser to the campaign, and Roger Stone, a longtime Republican operative.
The decision to open the investigations was not based on a dossier of salacious, uncorroborated allegations that were compiled by a former British spy working for a Washington research firm. The F.B.I. is also examining the allegations in that dossier, and a summary of its contents was provided to Mr. Trump earlier this month.
Of the half-dozen current and former officials who confirmed the existence of the investigations, some said they were providing information because they feared the new administration would obstruct their efforts. All spoke on condition of anonymity because they were not authorized to discuss the cases.
The F.B.I. investigation into Mr. Manafort began last spring, and was an outgrowth of a criminal investigation into his work for a pro-Russian political party in Ukraine and for the country’s former president, Viktor F. Yanukovych. In August, The Times reported that Mr. Manafort’s name had surfaced in a secret ledger that showed he had been paid millions in undisclosed cash payments. The Associated Press has reported that his work for Ukraine included a secret lobbying effort in Washington aimed at influencing American news organizations and government officials.