PANAMA CITY, SEPT. 13 -- Police today detained an American diplomat who was observing an antigovernment rally in which one protester was killed and five were wounded, rally organizers and the U.S. Embassy said.

The envoy, David Miller, a U.S. Embassy economic adviser, was released several hours later, according to the State Department in Washington.

The demonstration in the Panamanian capital's suburb of San Miguelito was broken up by about 15 men in civilian dress who fired at the crowd with handguns and shotguns, according to organizers, witnesses and a U.S. Embassy official who spoke on condition of anonymity.

It was the second protest in two weeks in San Miguelito in which unidentified men attacked the crowd and killed a civilian. Authorities had warned the organizers that future rallies would "not be permitted."

Miller had gone to watch the demonstration, embassy spokeswoman Cynthia Farrell said. Miller had gone to the site in a car clearly marked "U.S. Diplomatic Mission," the embassy sources said. He was detained at 5 p.m. EDT.

{A State Department spokeswoman said at 2 a.m. Monday that Miller had been released and that no charges had been filed against him.}

Panama is in its fourth month of protests against the military-backed government of President Eric Arturo Delvalle and military strongman Gen. Manuel Antonio Noriega.

The rally marked the second anniversary of the decapitation death of Hugo Spadafora, an opposition leader whose family blames the military for the killing.

Members of National Civic Crusade, an opposition coalition of 192 business, political, labor and student groups, estimated 5,000 people joined today's protest. Witnesses said there were far fewer.

Carlos Ernesto Gonzales, a coalition director, said the attackers first threw rocks and bottles, then opened fire on the crowd.

Gonzales identified the dead protester as Carlos Efrain Guzman, 49, and said he was shot in the head. Gonzalez and other witnesses said five other demonstrators were hospitalized with bullet wounds, including two shot in the leg.

No uniformed police or soldiers could be seen during the protest and attack. A duty officer at the Panama Defense Forces' National Investigations Department said the only official authorized to comment could not be located.