BOGOTA, Colombia (AP) — Colombian flags hung outside two bars in a symbol of defiance Sunday after a suspected rebel tossed grenades that killed a woman and wounded at least 72 people, including an American Airlines pilot.

Police blamed the Saturday night attack on the nation's largest rebel group, the Revolutionary Armed Forces of Colombia. They arrested a 25-year-old man they said threw the grenades at the Bogota Beer Company and Palos de Moguer, popular nightspots with locals and foreigners.

Besides the pilot, at least three other American citizens may be among the victims, said a U.S. official, speaking on condition of anonymity.

The United States has provided $2.5 billion to Colombia for its fight against rebels and drug traffickers, and the U.S. government is a supporter of hard-line President Alvaro Uribe, but it was unknown if the Americans were targets of the attack.

"It appears it was the FARC, like always," National Police Chief Gen. Jorge Castro told reporters. However, the U.S. official said it was too early to tell whether the attack was politically motivated or a personal vendetta.

Colombia's war pits the government and right-wing paramilitary groups against the Revolutionary Armed Forces of Colombia, or FARC, and a smaller rebel group in a conflict that kills about 3,500 people, mostly civilians, each year.

In a sign of defiance, a white banner reading "Never give in to the violent ones" hung outside Palos de Moguer.

"We cannot let the violence intimidate us," said owner Guillermo Alvarez Forero. "We want the bar to be as it always has been, a calm place where people come to drink in peace."

Expensive restaurants, a new shopping center and popular bars and dance clubs line the streets of the Zona Rosa, the downtown nightclub district. The two bars hit in the attack, both microbreweries, are generally packed on weekends.

The revelry ended about 11 p.m., police said, when the suspected rebel threw the first grenade at the Bogota Beer Company, where young people filled an outside patio. The grenade caused a second explosion in a gas-powered heat lamp, said a witness, Jose Ramon Marceles.

"I was stunned, I didn't know what had happened," said Marceles, a 26-year-old singer who was being treated at a nearby clinic for leg injuries. "Then, there was another explosion, and a huge flare-up that came from the heat lamp. Then everyone started running like crazy."

The suspected rebel then allegedly ran to the nearby Palos de Moguer and tossed the second grenade, which witnesses said landed on a cloth awning and started a fire. People knocked over tables and bar stools as they fled the flames.

The alleged rebel tried to shove his way through the crowds, but a security guard grabbed him and turned him over to police, said Bogota Mayor Antanas Mockus.

The FARC did not immediately issue any statement about the attack.

Since Uribe took office in August 2002, he has made defeating terrorism the principal goal of his administration. The FARC has responded by taking its fight to Colombia's big cities.

In February, the FARC detonated a car bomb at an exclusive Bogota nightclub, killing 36 people. In September, the rebel group set off a bomb on a motorcycle in front of a crowded nightclub in the city of Florencia, killing 13 people.

Six attacks have hit the capital this year alone, prompting people in Bogota to wonder if they are safe anywhere.

"It hurts my soul," Uribe said of Saturday's violence. "Against terrorism, there is only one road: to keep trying to fight it ... With persistence, we will succeed."

Customers at the bars wore pins of small Colombian flags on Sunday. At the Bogota Beer Company, workmen scrambled to repair windows and lay new brick on the patio.

Inside the bar, Juan Antonio Bravo, a peace activist, drank a soda and speculated that the rebels meant to target upper-class citizens who support Uribe.

"It's a way of them saying we are here, and we have power, and those of you in this society on the government's side are going to suffer," Bravo said.

Health officials confirmed that a German citizen was among the wounded, and said at least 18 of those injured were in critical condition Sunday.