美国有线新闻 CNN 美国在老挝遗留8千万颗未爆炸弹 奥巴马承诺援助9000万美元拆弹（在线收听）

First up, the remnants of a secret war. We're taking you to the Asian country of Laos. It's a landlocked communist nation located between Thailand and Vietnam. And during the Vietnam War, from the 1950s to the 1970s, Laos was fighting a civil war of its own. And the United States had a role in it.

In Vietnam, the U.S. supported South Vietnamese forces fighting the communist government of North Vietnam. In Laos, the U.S. supported southern Lao forces fighting communist forces in the north. The U.S. mission led by the Central Intelligence Agency dropped millions of tons of bombs on Laos.

But many of them did not explode and 43 years after the mission ended, some are still going off when people find or step on them. An average of 50 people in Laos are killed or maimed each year. And the presence of the bombs prevents much of the agricultural country from expanding its farmland.

Yesterday, the U.S. government pledged $90 million to help clear these bombs out. U.S. President Barack Obama, who's in Laos, made the announcement.

Andrew Stevens gives a sense of the challenge ahead.

ANDREW STEVENS, CNN CORRESPONDENT: For nine years until 1973, the U.S. carpet bomb Laos, trying to stop the communist insurgency and smashed North Vietnamese supply lines.

It was known as the Secret War. No American boots on the ground, just American bombs. More than two million tons of them rained down. Per capita, more explosives were dropped here than on any other country in history.

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STEVENS: And they're still exploding today.

This is a controlled detonation by the Mines Advisory Group which works in Laos to clear the bombs literally a few square yards at a time. Every patch of land has to be mapped and then swept.

Once detected, they zero in on the object and uncover it.

And this is what they usually find, clustered munitions known locally as bombies.

Up to 80 million of these failed to detonate and 1 percent of them have been cleared.

How long realistically with the resources at the country's disposal is it going to take to make this country safe?

NEIL ARNOLD, MINES ADVISORY GROUP (MAG): Currently with the resources, I'd say decades.

STEVENS: Decades?

ARNOLD: Yes.

(EXPLOSION)

STEVENS: And that is one more explosive device taken out, but across these plains, across these valleys and across these mountains, there are still tens of millions of threats remaining.