Desperate residents who said they heard voices coming from underground burrowed into the soil with their bare hands on Saturday night amid rumours that there were prisoners held somewhere deep below, setting off scenes of chaos.

A teacher at a nearby school told AFP it was widely believed that Kuwaitis captured after Iraq invaded its tiny southern neighbour in 1990, setting off the first Gulf War, were being held there.

"We are currently excavating extensively to prove either that there is something there or to bring some sort of closure," Captain Justin Prowse of the Scottish Black Watch regiment told AFP.

He said that there had been "no evidence so far apart from local information" to back up the claims that the sound of banging and voices had been heard, but said some basement cells had been found and that hooks were hanging from the ceilings.

He said that was not firm evidence of torture but it appeared that prisoners had been held in sub-human conditions. It was not immediately clear if the cells were part of a larger network linked to the courthouse nearby.

"The engineers are specialists and they now need a bit of space," Prowse said.

Two earthmovers and troops with high-powered drills had been sent to the site in the centre of the city. British forces sealed off the area after the crowd of around 300 tried to dig bare-handed Saturday evening, blocking the engineers from working.

Saddam's regime had always insisted it lost track of its Kuwaiti prisoners during an uprising by Shiite Muslims in southern Iraq after the 1991 Gulf War.

Kuwait on Saturday offered a reward to anyone who helps determine the fate of more than 600 people who disappeared during Iraq's occupation and said that it was actively cooperating with coalition forces to try to find them.

"We have no information on the whereabouts of the POWs after the fall of the Iraqi regime, but we hope for a speedy solution to end the suffering of the POWs and their families which has lasted for more than 12 years," said Foreign Minister Sheikh Sabah al-Ahmad al-Sabah.

Some families of Kuwait POWs expressed concern that the Iraqi regime, while battling US-led coalition forces, might take revenge on any Kuwaiti prisoners still held. Most prisoners were released under an amnesty by Saddam in October.

At Basra's police station the teacher, Abud Ali, said: "Other teachers and neighbours have heard sounds.

"This building was opened in 1968 but no one knows what is going on in there. There must be secret tunnels but even people who have worked here do not know all about them."

The scene Saturday night was one of frenzy as the crowd tried to tear into the ground with their fingers, while others tapped on a metal pipe leading underground to try to make contact with anyone down below.

SPACE.WIRE