OTTAWA, Ontario >> President Joe Biden said today that the U.S. would respond “forcefully” to protect its personnel after U.S. forces retaliated with airstrikes on sites in Syria used by groups affiliated with Iran’s Revolutionary Guard following a suspected Iranian-linked attack Thursday that killed a U.S. contractor and wounded seven other Americans in northeast Syria.

“The United States does not, does not seek conflict with Iran,” Biden said in Ottawa, Canada, where he is on a state visit. But he said Iran and its proxies should be prepared for the U.S. “to act forcefully to protect our people. That’s exactly what happened last night.” Activists said the U.S. bombing killed at least four people.

While it’s not the first time the U.S. and Iran have traded strikes in Syria, the attacks and the U.S. response threaten to upend recent efforts to deescalate tensions across the wider Middle East, whose rival powers have made steps toward détente in recent days after years of turmoil.

The Pentagon said a drone attack on a U.S. base Thursday killed a contractor and injured five U.S. troops and another contractor. That was followed by two simultaneous attacks on U.S. forces in Syria Friday, according to U.S. officials.

The officials said that based on preliminary information, there was a rocket attack Friday at a Conoco plant, and one U.S. service member was injured but is in stable condition. At about the same time, several drones were launched at Green Village, where U.S. troops are also based. One official said all but one of the drones were shot down, and there were no U.S. injuries there. The officials spoke on condition of anonymity to discuss military operations.

Two Syrian opposition activist groups reported a new wave of airstrikes on eastern Syria that hit positions of Iran-backed militias after rockets were fired at a Conoco gas plant that has a base housing American troops. Several U.S. officials, however, said the U.S. did not launch any attacks late Friday, and it wasn’t clear if the activists were referring to the attack on U.S. forces at Green Village.

U.S. Defense Secretary Lloyd Austin said the American intelligence community had determined the drone in Thursday’s attack on was of Iranian origin. U.S. officials said that conclusion was based on recovered debris and intelligence threat streams. They offered no immediate evidence to support the claim. The drone hit a maintenance facility at a coalition base in the northeast Syrian city of Hasaka.

In retaliation, the Pentagon said F-15 fighter jets flying out of al-Udeid Air Base in Qatar struck several locations around Deir el-Zour. Those strikes, said Austin, were a response to the drone attack “as well as a series of recent attacks against coalition forces in Syria” by groups affiliated with the Revolutionary Guard.

Biden, speaking during a press conference with Canadian Prime Minister Justin Trudeau, expressed his “deepest condolences” to the family of the American killed and well-wishes for the injured.

Iran relies on a network of proxy forces through the Mideast to counter the U.S. and Israel, its arch regional enemy. The U.S. has had forces in northeast Syria since 2015, when they deployed as part of the fight against the Islamic State group, and maintains some 900 troops there, working with Kurdish-led forces that control around a third of Syria.

Overnight, videos on social media purported to show explosions in Deir el-Zour, a strategic province that borders Iraq and contains oil fields. Iranian-backed militia groups and Syrian forces control the area, which also has seen suspected airstrikes by Israel in recent months allegedly targeting Iranian supply routes.

Reports on the number of killed and wounded in the U.S. strikes varied. Activist group Deir Ezzor 24, which covers news in the province, said four people were killed and a number of others were wounded. The Syrian Observatory for Human Rights, an opposition war monitor, said 11 Iranian-backed fighters were killed — including six at an arms depot in the Harabesh neighborhood in the city of Deir el-Zour and five at military posts near the towns of Mayadeen and Boukamal.

Rami Abdurrahman, who heads the Observatory, said three rockets were fired earlier Friday at the al-Omar oil field in Deir el-Zour that houses U.S. troops, an apparent retaliation to the American strikes.

The Associated Press could not immediately independently confirm the activist reports. Iran and Syria did not immediately acknowledge the strikes, and their officials at the United Nations in New York did not respond to requests for comment from the AP.

Iran’s paramilitary Revolutionary Guard, which answers only to Supreme Leader Ayatollah Ali Khamenei, has been suspected of carrying out attacks with bomb-carrying drones across the wider Middle East.

The exchange of strikes came as Saudi Arabia and Iran have been working toward reopening embassies in each other’s countries. The kingdom also acknowledged efforts to reopen a Saudi embassy in Syria, whose embattled President Bashar Assad has been backed by Iran in his country’s long war.

U.S. Army Gen. Erik Kurilla, the top U.S. commander for the Middle East, warned that its forces could carry out additional strikes if needed. “We are postured for scalable options in the face of any additional Iranian attacks,” Kurilla said in a statement.

On Thursday, Kurilla warned Congress during a hearing that the “Iran of today is exponentially more militarily capable than it was even five years ago.” He pointed to Iran’s arsenal of ballistic missiles and bomb-carrying drones.

“What Iran does to hide its hand is they use Iranian proxies,” Kurilla said.

According to officials, Iran has launched 80 attacks against U.S. forces and locations in Iraq and Syria since January 2021. The vast majority of those have been in Syria.

Diplomacy to deescalate the exchange appeared to begin immediately. The foreign minister of Qatar spoke by phone with U.S. National Security Adviser Jake Sullivan as well as Iranian Foreign Minister Hossein Amirabdollahian, the Qatari state news agency reported. Doha has been an interlocutor between Iran and the U.S. recently amid tensions over Tehran’s nuclear program.

The U.S. under Biden has struck Syria previously over tensions with Iran — in February and June of 2021, as well as August 2022.

Dareen Khalifa, a senior Syria analyst with the Brussels-based International Crisis Group, said that while Thursday’s exchange of strikes comes at a sensitive political moment due to the “overall deterioration of U.S.-Iran relations and the stalling of the nuclear talks,” she does not expect a significant escalation.

“These tit-for-tat strikes have been ongoing for a long time,” Khalifa said, although she noted that they usually do not result in casualties.

Since the U.S. drone strike that killed Revolutionary Guard Gen. Qassem Soleimani in 2020, Iran has sought “to make life difficult for U.S. forces stationed east of the Euphrates,” said Hamidreza Azizi, an expert with the German Institute for International and Security Affairs.

“Iran increased its support for local proxies in Deir el-Zour while trying to ally with the tribal forces in the area,” Azizi wrote in a recent analysis.

The strikes come during the Muslim holy month of Ramadan.

Syria’s war began with the 2011 Arab Spring protests that roiled the wider Middle East and toppled governments in Egypt, Libya, Tunisia and Yemen. It later morphed into a regional proxy conflict that has seen Russia and Iran back Assad. The United Nations estimates over 300,000 civilians have been killed in the war. Those figures do not include soldiers and insurgents killed in the conflict; their numbers are believed to be in the tens of thousands.