Blasts were heard at the headquarters of the National Oil Corporation (NOC) in the Libyan capital on Monday morning and a security operation is under way at the building, a witness told Reuters news agency.
Smoke could be seen rising from close to the NOC offices and security officials said they were attempting to deal with gunmen believed to have attacked the building.
Posts on social media showed photos of wounded people being carried from the scene, and security forces blocking the roads around the headquarters.
Tripoli was shaken by clashes between rival armed groups at the beginning of this month but the capital has also seen occasional attacks.
In May, Islamic State of Iraq and the Levant (ISIL, also known as ISIS) claimed a deadly attack on the national election commission offices in Tripoli.
More soon …