Intelligence officials in South Korea say the mysterious blast in North Korea may have been from a hydro-electric dam project, as Pyongyang claims. But doubts remain, and a team of foreign diplomats is expected to visit in the area in the next few days.

South Korean intelligence agents told the country's National Assembly that the mushroom cloud spotted by satellites could have been part of North Korean efforts to build a hydro-electric dam.

Pyongyang says it blew up a mountain last Thursday to make way for a dam.

Doubts remain. The South Korean spy agency says it cannot be certain about the cause of the blast. And experts on North Korea point out other possible explanations.

Kim Choong Nam is a North Korea specialist at the East-West Center, an independent think-tank in Hawaii.

"According to some South Korean experts, the area is actually a small stream and this is no place to build a dam," he said.

Pyongyang has offered to let diplomats from Britain and other countries visit the blast location. Britain's ambassador says the trip to the remote location will probably take place Thursday. He says North Korean officials seem intent on allowing the promised visit.

Many analysts also point out that the blast occurred late at night, an unusual time for a construction project explosion. The area is known to have many military facilities, including missile bases, and analysts say it is possible the blast was the result of an accident at one of them.

The blast initially raised concern that North Korea may have been testing a nuclear weapon. The United States, South Korea and other countries say there is no sign of such a test, although intelligence agencies in Washington think Pyongyang could be planning to hold a test soon.

The United States, China, Japan, South Korea and Russia are trying to persuade Pyongyang to abandon efforts to build nuclear weapons. Those efforts have stalled, as North Korea does not seem willing to hold a fourth round of talks this month, as originally planned.