It appears that rebels, in a convoy on the way to Brega, fired off an anti-aircraft gun in celebration and ended up getting attacked by NATO aircraft.

BBC:

The attack is thought to have happened between 2300 and midnight local time. There is very little clarity surrounding the incident, but an anti-aircraft gun may have been fired in celebration, our correspondent says.

A coalition plane then opened fire on the convoy, destroying the five vehicles, the rebels said.

Nato said it regretted any loss of civilian life.

"Nato jets are in the sky over Libya because they are enforcing the no fly zone, the UN mandate to protect civilians," Oana Lungescu told the BBC.

Nato spokeswoman Oana Lungescu: 'We are taking every care to ensure no human life is lost through Nato strikes'

But she added: "If someone fires against our aircraft they have the right to respond, they are enforcing a no fly zone. Any anti-aircraft guns would be acting against that."

At least 13 people were killed.

Meanwhile, John Rosenthal has dug up a document that should be getting more play on the internet. It was in Arabic, translated by Foundation for Defense of Democracy's Tony Badran, and is the original call for a "Day of Rage" in Libya.

No surprises - the motive of the demonstrators was not secular in the slightest but rather a call for jihad against Gaddafi.

Still wondering who we're fighting for in Libya?