Geneva police were "actively searching" for as many as four terror suspects Thursday as officials raised the security alert level in the city and surrounding areas.

The Associated Press reported that a CIA tip triggered the search linked to an investigation into the Paris massacre that left 130 people dead and hundreds of others wounded. But Sky News reported the search was not linked to Paris.

"As part of investigations conducted both internationally and nationally following the Paris attacks, Geneva police and its partners are actively searching for people flagged by the Confederation," the security department statement said, referring to the Swiss national government.

Geneva's security department added that city authorities received word that the "suspicious individuals who could be in Geneva or the Geneva region."

Police were increasing their deployments and counterterrorism vigilance level, and were working with international and national authorities to locate the suspects, the statement said. Authorities are looking for four people believed to be in the city, a security guard at the United Nations in Geneva told Reuters.

"We have gone from a vague threat to a specific one," Emmanuelle Lo Verso, a spokeswoman for the security department, told The Associated Press.

At the U.N. headquarters, security guards with MP5 submachine guns were stationed at entry points for cars.

"It is maximum alert," another U.N. guard told Reuters.

The Nov. 13 attacks on Paris, claimed by the Islamic State group, left 130 people dead and hundreds of others wounded. Salah Abdeslam, a fugitive suspected in the deadly attacks in Paris, is still at large. Several arrests were made in Belgium following the attacks.

One Swiss police official, speaking on condition of anonymity because he wasn't authorized to discuss the matter, told The Associated Press that Abdeslam wasn't among those being sought in Geneva.

Meanwhile, the head of a Serbian arms factory said one of the guns linked to Islamic militants in the Paris attacks was exported to the United States in 2013.

Milojko Brzakovic of the Zastava arms factory told the Associated Press Thursday that the M92 semi-automatic pistol was traced after its serial number matched the one delivered to an American arms dealer in May 2013.

At least seven of the weapons used or discovered after the attacks have been identified as produced by the Serbian factory, most of them manufactured before Yugoslavia broke up in a civil war in the 1990s.

Brzakovic said all those arms were delivered legally, but could have later found their way through illegal channels.

The Associated Press contributed to this report.