Rival Libyan militia groups have fought a gun battle in the capital, Tripoli, officials say.Exchanges of fire were heard and plumes of smoke seen coming from a district known as Tariq Al Shat in central Tripoli, eyewitnesses said.A BBC reporter who drove past the area later said the fighting had ceased.An interior ministry official told Reuters news agency the fighting was between militiamen from the city of Misrata, and a group from Zintan.The two militia groups fought together to overthrow Muammar Gaddafi last year.Several militias from outside the capital have set up bases in Tripoli and regularly clash as they fight for control of parts of the city.The country's interim National Transitional Council (NTC) is struggling to reassert its authority.The latest clashes took place near the coast, close to the Corinthia Bab al-Africa and Marriott hotels."Misrata controls a police academy building up the road and they are fighting with Zintan. We do not know why they are fighting," interior ministry Naji Awad told Reuters.