Liberian Rebels Meet Stiff Defense at Capital Airport : Civil war: The government also tells the BBC that it arrested an American in Monrovia and accused him of aiding the insurgents.

Rebel troops closed in on President Samuel K. Doe’s fortress-like mansion Saturday, trying to oust him before the arrival of a West African peacekeeping force.

They also moved to within 200 yards of Monrovia’s airport on the third day of a stepped-up offensive.

Meanwhile, the government announced that it had arrested an American and accused him of supporting the insurgents.

Fifty rebels of Charles Taylor’s National Patriotic Front, supported by 60-millimeter mortars and a 200-millimeter anti-aircraft gun, met stiff resistance from government troops using small arms to defend Spriggs Payne airfield.

No flights have been reported for several weeks at the airport, which is two miles from Doe’s fortified mansion. Taylor launched his offensive on Wednesday from Paynesville, a suburb on the eastern outskirts of Monrovia.

In a radio telephone call from Doe’s mansion to the British Broadcasting Corp., a presidential spokesman said the arrested American man was armed with a U.S.-made M-16 rifle and a loaded revolver when he was apprehended Friday in an apartment building in the eastern suburb of Sinkor.

He was tentatively identified as Andrew Voros of New Jersey, but the BBC reporter who took the call said the line was poor and it was difficult to understand the statement. The spokesman, whose name was not audible, accused the American of carrying out “rebel activities.”

Arrested with him was a Liberian army officer identified as Col. Christopher Doe, who was accused of working for the CIA. He is not related to President Doe.

In Washington, the State Department said the American was arrested at a guest house of the U.S. Agency for International Development, the government agency that administers the U.S. aid program worldwide.

The State Department said U.S. officials had been in contact with Doe’s aides but had received no response about what they planned to do with the man. A spokesman refused to identify him by name because he was a private citizen.

On Aug. 5, more than 200 Marines were airlifted to Monrovia to evacuate Americans and other foreigners. The Marines have since taken up defensive positions in the U.S. Embassy compound. The rest of the 2,100 Marines sent to Liberia are on U.S. warships cruising off Liberia’s coast.

West Germany said on Saturday that it has decided to close its embassy in Liberia. Bonn said it has contacted the United States about the best way to evacuate its 10 people and about 100 refugees and has asked Taylor to allow the evacuees to pass through territory he controls on their way out of the country.

The rebel advance comes as a five-nation West African peacekeeping force was mobilizing to sail to Monrovia from Freetown, capital of neighboring Sierra Leone. A contingent of 100 Nigerian troops arrived in Freetown by air Saturday.

Three Nigerian ships are waiting in Freetown to carry soldiers to Monrovia. Gambia announced it was sending a token company of 120 soldiers. Gambia has less than 1,000 soldiers and most are fighting a rebel insurgency.