A Libyan man on Thursday investigates the inside of the burned-out U.S. consulate in Benghazi after an attack that killed four Americans, including Ambassador Chris Stevens. Associated Press

BENGHAZI, Libya—The Libyan government arrested four people Thursday in connection with the deadly attack on the American consulate Tuesday night as Libyan and U.S. officials mounted a manhunt for others believed to be involved.

The Libyan government arrested four people Thursday in connection with the deadly attack on the American consulate Tuesday night as Libyan and U.S. officials mounted a manhunt for others believed to be involved. Matt Bradley has details on The News Hub. Photo: Reuters.

Hillary Clinton may have apologized for anti-Islam video but violent Middle East demonstrations against the U.S. continue to spread. WSJ's Matt Bradley reports from Cairo. Photo: AP

Protests spread across the region, breaking out in Yemen and Iran and once again in Cairo, where Egyptian police in riot gear beat back crowds of young men in a street filled with tear gas outside the U.S. Embassy.

Protests continued in San'a, Yemen, where demonstrators scaled the U.S. Embassy fence. Mohamed al-Sayaghi/Reuters

In Yemen's capital, San'a, hundreds of young men breached the outer security rings of the fortified U.S. Embassy. Evidently inflamed by a video mocking the Prophet Muhammad, one young man in Yemen shouted, "Troops will not stand in our way in defending the honor of our Prophet.'' Still, there were indications some demonstrators were using the protests to put pressure on their countries' governments as much as to assail the video.

Dhaka, Bangladesh Reuters

In the U.S., Secretary of State Hillary Clinton denounced both the anti-Islam video and the violence in Libya that took the life of U.S. Ambassador Christopher Stevens and three other Americans earlier this week. Emphasizing that the U.S. government had no role in the video, she called it "reprehensible" and said "we absolutely reject its content and message." At the same time, she said, there was "no justification—none at all—for responding to this video with violence."

As U.S. officials struggled to gain a clear picture of who was behind the mob attack in Benghazi late Tuesday, U.S. intelligence agencies were increasingly skeptical it was planned in advance, a shift from an initial assessment by some. U.S. officials also were increasingly doubtful the militants had direct ties to al Qaeda.

The information pointing to the possibility of a more spontaneous assault could deflect criticism of both the U.S. and Libyan governments for missing clues to an impending attack. An impromptu attack without clear ties to a major terrorist organization also could ease pressure on U.S. officials to respond aggressively.

The third and fourth Americans killed in the attack on the U.S. consulate were identified by the State Department late Thursday as security personnel Tyrone S. Woods and Glen A. Doherty, both former Navy SEALs. Previously identified, in addition to Mr. Stevens, was State Department information officer Sean Smith.

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The events continued to reverberate in the U.S. presidential campaign, in a more muted form than on Wednesday. Republican Mitt Romney didn't repeat his criticism that the Obama administration was "effectively apologizing for the right of free speech" but said in Fairfax, Va., that the Libyan attack showed that "a strong America is essential to shape events."

Cairo Amr Abdallah Dalsh/Reuters

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President Barack Obama, campaigning in Colorado, promised that "no act of terror will go unpunished.'' Mr. Obama also has led a U.S. effort to moderate the reaction to the film in Muslim countries and stem protests in advance of Friday prayers, which often lead to new demonstrations in Muslim lands.

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Past attacks on U.S. embassies and consulates around the world.

Turmoil Spreads


A protester shouted slogans during clashes with riot police along a road leading to the U.S. Embassy in Cairo Friday. Reuters

A Libyan official in charge of a task force tracking a militant group whose members led the first wave of attacks said his country was throwing all available resources into the hunt. Wanis al-Sharif, a deputy interior minister, said his team was using telephone taps, among other tools, to follow the group, hoping for a better understanding of its strength and structure.

"There is a group now that is under our custody, but there is a group we're following to know who's connected to them, and [we] are monitoring their phone calls," Mr. Sharif said, declining to provide more details.

The U.S. role in the manhunt has remained low key, in part out of concerns that a heavy overt American role would inflame tensions. But the U.S. has ramped up intelligence collection in the region, using unmanned aerial drones and other sophisticated eavesdropping equipment, officials said.

The distinctive humming motors of drones could be heard in the skies above Benghazi Thursday. The U.S. has used drones and other intelligence-collection efforts since the fall of Col. Moammar Gadhafi to track militant camps and weapons caches in areas east of Benghazi known to be Islamist hotbeds.

The focus of the Libyan probe appears up to this point has been an Islamist rebel brigade called Ansar al Sharia, a group of fundamentalist religious men who banded together in a militia last year in the fight to oust Gadhafi. Members of the group were at the consulate attack and cars belonging to members were found abandoned in the area, according to Mr. Sharif. It isn't known whether the four men arrested are members of the group.

A spokesman for Ansar al Sharia, Hani Mansouri, said at a news conference Thursday that his organization didn't organize or participate in the attack.

U.S. officials said preliminary information suggests the militants saw protests sparked by an anti-Islamic video as an opportunity to wreak havoc on a prominent symbol of the U.S. to make an anti-American statement. "There is no intelligence indicating this was premeditated," a U.S. official said. "It looks like it was an opportunistic attack by a group in the region."

There also are no indications at this point that the attackers knew the ambassador was in the building.

Around Benghazi, Libyan forces made no discernible ramp-up of security. A unit of six lightly armed Libyan defense soldiers stood outside the burned-out consulate complex Thursday afternoon.

The siege began late Tuesday night. New descriptions by Libyan security officials detailed hours of terror in which outgunned consulate security forces tried in vain to battle well-armed assailants.

Dilan Samo, right, and Jeje Barwary hold photos during a candlelight vigil in honor and memory of slain American Ambassador to Libya Christopher Stevens outside the permanent mission to Libya in Manhattan on Thursday. Kevin Hagen for the Wall Street

Mohammed Farraj, a soldier who was part of a four-member Libyan military unit permanently stationed at the facility. said he heard commotion on the dirt road outside the compound about 8:30 p.m. and was told by walkie-talkie of a group of armed, bearded protesters gathering.

There also were four private security guards, all Libyans, who weren't armed and worked inside the compound. Interviews with the Libyans indicated there also were four to eight American security guards around the compound when the attack started.

As trouble began, two Libyans posted on the outside moved inside and alerted the Libyan security forces, said Mr. Farraj, but backup didn't arrive immediately. Mr. Sharif said that he advised the armed security unit not to open fire so as to not inflame the situation.

Stream: Libya Attack

Follow real-time coverage of the attack in Libya against the U.S. embassy and the unfolding unrest.

Fighting erupted at about 9:30 p.m., said Abdulaziz Mezhbury, who works for a Libyan-British security firm called Blue Mountain and was responsible for security around the main villa. Mr. Mezhbury faced a storm of grenades and small-arms fire from militants who had breached the 12-foot wall around the compound. He was shot three times in the leg and suffered shrapnel wounds from grenades.

As the compound was being overrun, the Americans started returning fire, said Mr. Farraj. "But we were totally outgunned. I called more of the brigade to come reinforce us." He said a lull developed around 11 p.m. and the Americans and Libyan military appeared to be back in control. At this point, Mr. Farraj said, he believed that the bulk of the American consulate staff were evacuated. But the ambassador was missing and the villa was on fire.

The security guards made a decision to brave the flames to find the missing ambassador but were beaten back by the fire and couldn't find Mr. Stevens.

—Julian E. Barnes, Siobhan Gorman and Hakim Almasmari contributed to this article.

Write to Margaret Coker at margaret.coker@wsj.com