TRIPOLI (Reuters) - Muammar Gaddafi's son Mo'tassim was captured in Sirte on Wednesday while trying to escape the town, the head of the Tripoli Revolutionary Council said.

"He was arrested today in Sirte," Colonel Abdullah Naker told Reuters.

He was taken to Benghazi where he was questioned, other ruling National Transitional Council (NTC) sources based in Sirte and Benghazi said. They said he had been caught as he tried to leave Sirte in a car with a family.

NTC sources had earlier told Reuters that Mo'tassim, formerly Libya's national security adviser, had been captured on Tuesday.

Celebratory bursts of machinegun fire and fireworks lit up the skies over the capital Tripoli as reports of Mo'tassim's capture circulated.

Military sources said he was being held in the Boatneh military camp in Benghazi and that he was "exhausted" but uninjured.

Another senior NTC military official told Reuters that Gaddafi's son had cropped short his usually longer hair in an attempt to disguise himself. He is so far the only member of Gaddafi's immediate family to be captured by the NTC forces who have led the successful rebellion.

Muammar Gaddafi, Libya's ousted leader of 42 years, and his most politically prominent son, Saif al-Islam, have been on the run since the fall of Tripoli on August 23.

Gaddafi's daughter Aisha, her brothers Hannibal and Mohammed, their mother Safi and several other family members fled to Algeria in August and have been there since.

Another son, Saadi, is in Niger.

Most of Sirte, Gaddafi's hometown, has been captured by fighters loyal to the NTC in recent days after weeks of siege.

Interim government officials had said they believed Mo'tassim was hiding in the city's hospital.