An armed group guarding a major Libyan oil field attacked the headquarters of the Petroleum Facilities Guard in Tripoli on Tuesday, and one person was killed and five were wounded in the violence, the oil force said.

In a statement on its Facebook page, the Petroleum Facilities Guard, which secures Libya's oil facilities, said the armed men were from the western mountain town of Zintan and were among guards who protect the Sharara oilfield. Sharara can pump around 350,000 barrels per day.

"A group of armed men came to attack the headquarters. We tried to defend it and there were clashes," Colonel Ali Elahrash, of the PFG, said.

"Everything is now under control."

A source within the force said the men were said to be disgruntled after another group was given supervision of a drill in the area, but this could not immediately be verified.

Members of the Zintan group could not immediately be reached for comment.

The PFG statement said five people were injured in the fighting including three bystanders and two members of the oil force. Elahrash later told Reuters one bystander had been killed in the violence, which ended after backup - from the oil force and national guard - came to oust the attackers from the headquarters in the southern outskirts of the capital.

"The attackers went onto the roofs of nearby buildings and started shooting. They also used heavy weapons," the statement said. It added there had been negotiations with the men before the clashes but gave no further details.

The Zintan group was said to have fled to a compound, where an angry crowd later gathered following the death of the bystander, Elahrash said. Clashes then broke out between the crowd supported by armed militias and the Zintan group.

"The fighting is quite heavy," he said.

The PFG operates under the official remit of the Defence Ministry, but only about 2,000 of its 15,000 members have had training from the military.

The rest are former rebels who fought to oust Muammar Gaddafi in the North African country's 2011 war.

Ill-trained and using weapons left over from the conflict, the men have fought amongst themselves in the past, causing disruptions at oil facilities.