The ousted Libyan dictator Muammar Gadaffi and his sons may have evaded capture by fleeing through waterpipes large enough to hide military vehicles, rebel commanders believe.

The pipes of the Great Manmade River project, designed to supply Libyan coastal cities with water from a huge natural reservoir beneath the desert, are up to 13ft in diameter, the largest built. They would provide excellent cover from Nato spy planes, which have joined the hunt for Gadaffi in the past week, according to two senior advisers on the rebel military council in Tripoli.

Gadaffi’s greatest engineering feat runs for 328 miles south from the town of Bani Walid, southeast of Tripoli, to a point just north of the oasis town of Sabha. It could double as an underground bunker for the scud missiles, rocket launchers and grad missiles that Gadaffi is still believed to possess, the advisers said.

Rebels believe that Gadaffi, whom they say was last seen making a telephone call from Bani Walid’s small airport, has fled through the pipes towards Sabha while thousands of Libyan army soldiers block the rebels’ advance south.

The $33 billion (£20 billion) pipeline project was begun in 1984 and three of its five phases are complete, supplying water to much of the country. But supplies to western Libya, including Tripoli, were shut down on August 21, fuelling speculation that the fleeing dictator had a military purpose for the network.

During the past week rebel forces have massed on the outskirts of Bani Walid.

They have been pursuing the former Libyan leader and his sons since storming the capital on August 20. But days of heavy fighting in Tripoli, followed by a flurry of negotiations between the rebels, tribal elders and the Gadaffi family slowed down the hunt as Nato monitored Libyan troop movements in the south of the country.

Gadaffi’s wife Safia, his daughter Aisha and sons Mohammed and Hannibal fled last week to Algeria. Rebel commanders believe there is still a chance that Gadaffi himself and at least two other sons at large in Libya — Saif al-Islam and Saadi — will surrender. Others say Gadaffi will have used this week’s lull in fighting to move closer to the borders with Niger, Chad, Algeria and Sudan.

“He’s wily like a fox,” said one adviser to Mehdi al-Harati, second-in-command of the Tripoli military council. “We always knew this would be his tactic, but we’re worried about causing civilian casualties in some of these towns. It may spark tribal war if we went in heavy-handed.”

As they pushed into Tripoli, rebel commanders expected Gadaffi to embroil them in street fighting while making his escape.

On August 25 rebel forces were still pinned down in the capital’s poorer neighbourhoods of Bosleem and Al Hadba, which are renowned for harbouring pro-Gadaffi loyalists.

Fighting also erupted in the nearby zoo, with rebels using machineguns mounted on pick-ups to fight army troops among the trees.

Further resistance sprang up as the rebels continued to push the Libyan army towards the southern outskirts of the city. Snipers and African mercenaries were said to have held up the rebels, allowing the Gadaffis to make a protected withdrawal.

The following day, as fighting continued to rage in the two neighbourhoods, Muammar Gadaffi drove into the headquarters of the Khamis Brigade in southern Tripoli, according to one adviser linked with Nato intelligence.

There he met his son Khamis and pregnant daughter Aisha.

They kept their meeting short as rebels encircled the headquarters. While machinegunners laid down covering fire, Gadaffi and Aisha jumped into two Toyota Land Cruisers and sped south in a 30-car convoy, the adviser said.

Gadaffi’s convoy made for Bani Walid, 90 miles away and home to the once pro-regime Warfalla tribe.
“The family’s plan was simple,” an adviser said. “Khamis would stay to defend the retreat while the other sons and Aisha fled south. By entering Warfalla land the Gadaffis wanted to start a tribal war.”

The rebels believed Gadaffi wanted to suck their men into Bani Walid, triggering clashes inside the town that would unite the powerful Warfalla clan against the rebel army.

The plan would fail: the rebels remained patient, preferring to negotiate a truce with the Warfalla tribe.

The rebel army first attempted to pursue the Gadaffis. Scouts on the road ahead tipped off fighters stationed on the outskirts of Tarhuna, halfway to Bani Walid, about the approach of a large convoy of ammunition trucks, antiaircraft guns and pick-up trucks led by Khamis Gadaffi.

As the convoy approached, the rebels hiding by the road opened fire with machineguns and rocket-propelled grenades, according to Colonel Kalid Nahji, the commander of rebel forces in Tarhuna. Several armoured Toyotas were engulfed in flames, killing 13 people. More than a dozen others were captured, Nahji said.

Testimony from the prisoners suggests that Khamis was killed in the firefight, but other rebels question these reports.

“We’re not sure if we got Khamis, but they buried someone senior in secret that evening in Bani Walid,” said Dr Abdullah Kenshil, who heads the political wing of the Bani Walid brigade. “They buried the body quickly and only security attended. We believe it was either Khamis or the intelligence chief’s son.”

By nightfall on August 27 Gadaffi had entered Bani Walid, according to Kenshil, who said his information came from a network of rebel spies inside the city.

Residents woke to a large presence of Libyan soldiers positioned in buildings inside the town, on the streets and in the surrounding villages, Kenshil said.

Meanwhile, Saif, the British-educated son who was once regarded as Gadaffi’s most likely successor, made numerous telephone calls to an intermediary. This man was in touch with several American lawyers representing Saif in Tripoli, according to one lawyer.

“Saif wants to negotiate his surrender,” the lawyer said. “He doesn’t want to be tried in Libya. He wants to be handed over to the International Criminal Court if he’s captured.”

Telephone calls from Saadi Gadaffi, who was also believed to be hiding in Bani Walid at the time, were then made to Harati, the deputy head of Tripoli’s military council, pleading for leniency.

“He was very scared,” said Harati. “He wanted Saudi Arabia and the United Nations to oversee the terms of his surrender.”

When news of the negotiations broke in the media, however, a team from Saudi Arabia which had been due in Tripoli on Wednesday cancelled their visit.

That day rebel spies inside Bani Walid spotted Gadaffi making the telephone call from a landline at the airport, according to Kenshil. Rebels believe the call was made to a television station in Syria, which broadcast the ousted dictator’s warning to the Libyan people that he would never surrender.

Two days later Gadaffi left Bani Walid and headed south for Sabha in a convoy of six armoured Land Cruisers, according to rebel spies.

Meanwhile, Saif was spotted strolling through the centre of the town flanked by bodyguards as he tried to rally residents, Kenshil said.

The following day the head of the Warfalla told the remaining members of Gadaffi’s family that his tribe could no longer guarantee their safety.

On Thursday Libyan troops began to withdraw from the town and the surrounding villages before heading south with a convoy of armoured vehicles believed to be carrying Saif, according to Kenshil and his spy network.