"One of the main organisers of the Paris terror attacks was in Keleti station in Budapest, recruiting a team from immigrants who had refused to register with Hungarian authorities," said Prime Minister Viktor Orban's chief of staff Janos Lazar, referring to migrants.
He then left "the country with them," Lazar told a regular news conference in Budapest.
Lazar did not name the man or say when he was in Hungary, nor whether those he picked up went on to take part in the November 13 atrocities in the French capital claimed by the Islamic State (IS) extremist group.
"We do not have information that can be made public," Hungary's counterterrorism police TEK told AFP by email Thursday.
But a French source familiar with the overall investigation told AFP that a car rented by Salah Abdeslam, one of the alleged Paris assailants currently on the run, is known to have been in Hungary on September 17.
It was unclear, however, whether Belgian-born Abdeslam -- who played a key logistical role in the Paris attacks in which 130 people were killed -- was himself in the vehicle, and if so, whether he was accompanied, the source added.
Abdeslam, 26, was also registered as having been in Austria on September 9 after being stopped in a routine traffic check, Austrian authorities said on November 17.
He and two other men were stopped in a car with Belgian number plates after travelling south from Germany, not west from Hungary.
Abdeslam told police he was "on holiday".
Austrian authorities last month said that the two others "have so far not been named in connection" with the Paris attacks.
Until mid-September, when Hungary sealed its border with Serbia, thousands of migrants and refugees spent days or even weeks in makeshift camps at Keleti station on their way to northern Europe after travelling up through the Balkans.
Abdeslam, whose brother Brahim blew himself up in a bar the night of the attacks, was spirited away from Paris to Belgium after the November 13 massacre by two other men who were later arrested and charged there.