Libyan rebels say they know where former leader Muammar Gaddafi is hiding, and it is only a matter of time until he is captured or killed.

Spokesman Anis Sharif said Gaddafi was still in Libya, and had been tracked using human intelligence and technology .

He refused to say where he was, but said he was trapped in a 40-mile-radius area surrounded by rebels.

"He can't get out," Mr Sharif said, adding that the rebels were preparing to either detain him or kill him.

Locating Gaddafi would help seal the new rulers' hold on the country.

Convoys of Gaddafi loyalists fled across the Sahara into Niger earlier this week.

Some rebels depicted the flight to Niger as a major exodus of Gaddafi's most hardcore backers. But confirmed information on the number and identity of those leaving was scarce given the vast area of desert - over 1,000 miles - between populated areas on the two sides of the border.

In Niger's capital, Niamey, a spokesman for the president said that Gaddafi's security chief had crossed the desert into Niger on Monday accompanied by a major Tuareg rebel.

The government of Niger dispatched a military convoy to escort Mansour Dao, the former commander of Libya's Revolutionary Guards who is a cousin of Gaddafi as well as a member of his inner circle, to Niamey.

Dao is the only senior Libyan figure to have crossed into Niger, said the spokesman, who denied reports that Gaddafi or any member of his immediate family were in the convoy.

Since Tripoli's fall last month to Libyan rebels, there has been a movement of Gaddafi loyalists across the porous desert border that separates Libya from Niger. They include Tuareg fighters who are nationals of Niger and next-door neighbour Mali who fought on Gaddafi's side in the civil war.

There has been intense speculation regarding the whereabouts of Gaddafi's inner circle and last week, Algeria, which like Niger shares a border with Libya - confirmed that the former leader's wife, his daughter, two of his sons, and several grandchildren had crossed onto Algerian soil.

The West African nation of Burkina Faso, which borders Niger, offered Gaddafi asylum last month, raising speculation the convoys were part of plan to arrange passage there for him. But on Tuesday, Burkina Faso distanced itself from Gaddafi, indicating he would be arrested if he went there.