The communications of Trump transition officials - possibly including President Donald Trump himself - may have been "monitored" after the election as part of an "incidental collection", the chairman of the House intelligence committee said.
Speaking to reporters on Capitol Hill, Republican Representative Devin Nunes said the intercepted communications do not appear to be related to the ongoing FBI investigation into Trump associates' contacts with Russia.
He said he believes the intelligence collections were done legally.
The White House said Mr Nunes would brief Mr Trump on the matter later.
It was unclear whether Mr Trump's own communications were specifically monitored.
Mr Nunes initially said "yes" when asked if Mr Trump was among those swept up in the intelligence monitoring, but then said it was only "possible" that the president's communications were picked up.
Mr Nunes said the information on the Trump team was collected in November, December and January, the period after the election in which Mr Trump was holding calls with foreign leaders, interviewing cabinet secretaries, and was beginning to sketch out administration policy.
Mr Nunes said the monitored material was "widely disseminated" in intelligence reports.
Asked whether he believed the transition team had been spied on, Mr Nunes said: "It all depends on one's definition of spying."
The California congressman did not say how the Trump team's communications were picked up.
US intelligence agencies routinely monitor the communications of foreign officials.
That surveillance sometimes includes the name of an American that the foreigner is speaking to or about.
When this happens, intelligence analysts are obliged to hide or "minimise" the name of the American, unless knowing the American's name is necessary to understanding the foreign intelligence described in the report.
Mr Nunes said the names of Trump associates were "unmasked" after the incidental collection, though he did not identify those aides.
Those aides are believed to include Michael Flynn, who was fired as White House national security adviser after misleading Vice President Mike Pence and other top officials about his contacts with Russia's ambassador to the United States.
Mr Nunes would not say how he had received the new information.
Mr Nunes notably did not appear alongside Representative Adam Schiff, the intelligence committee's top Democrat.
A Schiff spokesman said Mr Nunes had not informed his Democratic counterpart before disclosing the new information publicly.