FBI agents in Puerto Rico on Friday searched five homes and a business to thwart what the agency said was a "domestic terrorist attack" planned by militants favoring independence for the U.S. island territory.

The alleged attack would have involved explosives directed at "privately owned interests" and the public in Puerto Rico, according to Luis Fraticelli, special agent in charge of the FBI on the island.

Fraticelli's statement did not disclose details about the alleged attack or the investigation, which the FBI earlier said was focused on the pro-independence People's Boricua Army.

FBI spokesman Harry Rodriguez said there were no arrests, but declined to provide details.

The People's Boricua Army, also known as the Macheteros or "cane cutters," was accused of bombings and attacks in the 1970s and 1980s. The group was among three to claim responsibility for a 1979 attack in which gunmen opened fire on a U.S. Navy bus, killing two U.S. sailors.

In September, FBI agents shot and killed Filiberto Ojeda Rios, a leader of the Macheteros who was wanted for the 1983 robbery of an armored truck depot in Connecticut, after he allegedly opened fire when they came to arrest him at a farmhouse in a western town on the island.

Hundreds of protesters staged a demonstration late Friday outside the federal building in San Juan, accusing the FBI of persecuting the pro-independence movement.

They burned an American flag and chanted, "If the Yankees don't leave, they'll die in Puerto Rico!"

"I believe that this is an act of abuse and an act of persecution," said Alberto Jesus, known for leading protests against U.S. Navy bombing exercises on Vieques island. "We have here a foreign country that puts the label of terrorist on us."

As word spread of the FBI operation early Friday, protesters and reporters gathered outside an apartment building in San Juan as it was searched by agents.

A local television station broadcast images of federal agents using pepper spray on reporters and protesters.

Fraticelli said agents used "non-lethal force" when protesters and the media tried to cross a law enforcement perimeter. The move was necessary "to protect members of the media, the public and the law enforcement officers executing this lawful search warrant."

Gov. Anibal Acevedo Vila denounced the incident, saying in a statement that there was "no justification for the excessive use of force."