The military of the Democratic Republic of Congo said on Sunday that it had foiled a coup attempt involving foreigners, hours after a gunfight near the presidential palace in which at least three people were killed.

In a brief statement on state television, an army spokesman, Brig. Gen. Sylvain Ekenge, initially offered little detail about the purported putsch in the capital, Kinshasa, other than to say that the plotters and their leader had been “put out of action.”

But he later told The Associated Press that three Americans were among the perpetrators, and the United States ambassador to Congo, Lucy Tamlyn, acknowledged publicly that American citizens may have been involved.

The United States will cooperate “to the fullest extent” with the Congolese authorities “as they investigate these criminal acts and hold accountable any U.S. citizen involved.,” she said on X, formerly Twitter.

Her statement came hours after videos circulated widely on social media showing a white man with a bloodied face sitting at the feet of Congolese soldiers — one of three Americans the military accused of involvement.

President Felix Tshisekedi, who was re-elected for a second term after a chaotic vote in December, was unharmed in the incident. But its brief and apparently confused nature, as well as many incongruous details, left many Congolese puzzled on Sunday and triggered intense speculation about who was behind it, or whether it was even a genuine coup attempt.

A wave of military takeovers in central and western Africa in recent years has caused alarm in Washington because they have undermined democracy in the region and given Russia opportunity to increase its influence. In Niger, where the military seized power last August, the government is pressing the United States to withdraw its troops from bases where Russian personnel have started to arrive.

Congo is a focus of American policy in Africa for its deep reserves of cobalt, a key mineral in the production of electric vehicles. China owns or controls most of Congo’s cobalt-producing sites, a source of concern to the Biden administration.

But while most of the region’s recent coups have been led by senior military officers from those countries, the purported one in Kinshasa on Sunday appeared to have been led by an obscure opposition politician based in the United States, and appeared to have little prospect of succeeding.

It started around 4:30 on Sunday morning when a group of armed men attacked the Kinshasa residence of Vital Kamerhe, a legislator and a candidate to be speaker of the National Assembly, which is based just over a mile from the presidential palace.

A gunfight erupted in which two police officers and one assailant were killed, a spokesman for Mr. Kamerhe and, separately, Japan’s ambassador to Congo, said on social media.

The assailants then moved toward the presidential palace, the Congolese news media reported. At the same time Christian Malanga, an exiled opponent of the Congolese government who runs a minor opposition party, posted a livestream video in which he appeared to be leading the attack.

The video, which The Times could not verify independently, showed Mr. Malanga, 40, surrounded by men in military uniform, some with American flags affixed to their vests. “Felix, you’re out,” he said. “We are coming for you.”

But when the assailants reached the nearby presidential palace, soldiers intercepted and arrested them, according to the military and local media reports. Images of Mr. Malanga’s body later circulated, and General Ekenge, the army spokesman, told The A.P. that he had been killed while resisting arrest.

The names of the suspects were not immediately released, but images on social media provided clues.

In addition to the footage of a bloodied white man on the ground, sitting beside someone identified as Mr. Malanga’s son, an American, images also circulated showing the passport of another American, Benjamin Reuben Zalman-Polun, said to be involved in the episode. News reports previously identified him as a cannabis entrepreneur involved in gold mining with Mr. Malanga.

Dino Mahtani, a former United Nations investigator on Congo, said the Congolese authorities told him in 2018 that they suspected Mr. Malanga of a plot to kill the previous president, Joseph Kabila.

President Tshisekedi did not appear to be in any immediate danger on Sunday; he is well known to live miles from the presidential palace, at his residence in another part of the city.

A website in Mr. Malanga’s name said that his family settled in Salt Lake City in the 1990s as part of a refugee resettlement program. He participated in the U.S. Army Junior Reserve Officers’ Training Corps, it said.

He returned to Congo to run for political office in 2011 but was arrested “on bogus charges” and held for several weeks by police officers who beat him, it said.

A year later, he returned to the United States, where he formed the United Congolese Party, “a grass-roots platform that unifies the Congolese diaspora around the world opposing the current Congolese dictatorship,” the site said.