About 100 Libyans surrounded a Tunisian passenger aircraft at one of the capital's airports on Saturday, delaying its takeoff in a protest at the government.
Witnesses said about a dozen cars drove out on to the tarmac at Tripoli's Mitiga airport and blocked a Tunisair Airbus A300 jet, with passengers on board, from moving.
The incident was the latest sign of lawlessness in Libya, where the interim authority in power since Muammar Gaddafi was ousted, the National Transitional Council (NTC), is struggling to control disparate local interests, many of them backed by armed militias.
The protesters were from the Souq al-Juma district of Tripoli, a stronghold of anti-Gaddafi sentiment during the uprising against his rule.
They said they wanted the Libyan government to open an investigation into a clash last week in which several members of the Souq al-Juma militia were killed.
The clash happened in Bani Walid, a town southeast of Tripoli which was a pro-Gaddafi bastion and one of the last places to submit to the new Libyan leadership.
"People are protesting over the slow action that the NTC is taking over this. They are putting pressure on the NTC to take action, and make their message known," said Abdulrazzaq El-Aradi, NTC member for Souq al-Juma.
A spokeswoman for Tunisair said none of the passengers were harmed.
She said some of the protesters had tried to board the aircraft but the captain had shut the door and barred them entry. She said armed men had said they wanted to check the identity of some injured Libyans on board the plane.
A Reuters reporter at Mitiga airport said there was no sign of violence. A few of the protesters had weapons and wore combat fatigues, but most of them were civilians.
"This is a peaceful protest. The plane is intact. The passengers are okay. We do not want to harm anybody," Hosni Berbesh, dressed in fatigues, said.
He said the aim of the protest was to "explain to the government that we have a request, that the government should respond to us".
A Tunisair spokeswoman said the plane later took off with 54 passengers on board. She said some Libyan passengers had chosen to get off the plane, without giving details.