MONROVIA, Liberia (AP) _ Troops at a roadblock near the presidential mansion opened fire Friday on an American, who died while undergoing surgery for his wounds, the U.S. Embassy said.

Also Friday, the government said rebels in an eastern war zone ambushed a freight train and three people aboard were reported kidnapped, including the West Africa correspondent for the U.S. news agency United Press International.

The developments occur at a time when relations between the United States and this West African nation founded by freed American slaves are at their lowest level since President Samuel Doe seized power in a bloody April 1980 coup.

The U.S. statement said soldiers manning a roadblock near Doe's residence in Monrovia, the capital, opened fire after midnight on a vehicle driven by Martin Joseph Millay, wounding him in the leg.

Millay suffered a heart attack and died during surgery for his wounds, the statement said. A U.S. Embassy official, reached by telephone from Abidjan, Ivory Coast, said he did not know Millay's age or hometown, only that he worked for a small charter airline, Gibacol Air Services.

Last week, an elderly American missionary and his British wife were killed in a shootout between Liberian troops and rebels in eastern Nimba county. It was not known who killed the Rev. Tom Jackson and his wife, June. They were Protestant missionaries who had worked in Liberia for 40 years.

In addition, two U.S. Embassy warehouses in Monrovia were gutted in a March fire that destroyed $3 million worth of goods. Embassy officials suspect arson.

Acting Information Minister Moses Washington told reporters Friday that rebels ambushed a train carrying empty iron ore carts from the port of Buchanan to a state-owned mine in Yekepa, Nimba county.

The rebels demanded food from the conductors and three passengers, including Mark Huband, a Briton who was UPI's West African correspondent and also worked for the London Financial Times.

One of the conductors escaped, but the whereabouts of the other people on the train was unknown, the minister said.

Huband, 26, had been on assignment from Abidjan, where he is based, a UPI spokesman said Friday night from Washington.

Rebels fighting since December to overthrow Doe had threatened to blow up the train for the Yekepa mine, a well-guarded complex in the north of Nimba County managed by foreigners, including Britons and Americans.

The United States, which in the past has been a major supporter of Doe, cut aid to Liberia this year, citing human rights violations and failure to repay debts.