A strike Thursday by a suspected Iranian-made drone killed a U.S. contractor and wounded five American troops and another contractor in northeast Syria, the Pentagon said. American forces said they retaliated soon after with "precision airstrikes" in Syria targeting facilities used by groups affiliated with Iran's Revolutionary Guard, with activist groups saying they killed at least four people.
The attack 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.
U.S. Defense Secretary Lloyd Austin said in a statement that the American intelligence community had determined the drone was of Iranian origin, but offered no other immediate evidence to support the claim.
"The airstrikes were conducted in response to today's attack as well as a series of recent attacks against coalition forces in Syria" by groups affiliated with the Revolutionary Guard, Austin said.
Iran relies on a network of proxy forces through the Mideast to counter the U.S. and Israel, its arch regional enemy.
The Pentagon said two of the wounded service members were treated on-site, while three others and the injured contractor were transported to medical facilities in Iraq.
Overnight, videos on social media purported to show explosions in Syria's Deir el-Zour, a strategic province that borders Iraq and contains oil fields. Iran-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.
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Iran and Syria did not immediately acknowledge the strikes, nor did their officials at the United Nations in New York respond to requests for comment from The Associated Press.
The activist group Deir Ezzor 24 put the death toll from the American strikes at four people. Deir Ezzor 24, which covers news in Deir el-Zour province, said the strikes hit the city of Deir el-Zour as well as militiamen posts near Mayadeen and Boukamal. It said the strikes also wounded people, including Iraqis.
The Syrian Observatory for Human Rights, an opposition war monitor, reported that the American strikes killed six Iranian-backed fighters at an arms depot in the Harabesh neighborhood in the city of Deir el-Zour. The Observatory, which relies on a network of local contacts in Syria, said U.S. bombing at a post near the town of Mayadeen killed two fighters.
A separate American strike hit a military post near the town of Boukamal along the border with Iraq, killing another three fighters, the Observatory said.
The AP could not immediately independently confirm the activist reports.
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.
In recent months, Russia has begun using Iranian drones in its attacks on sites across Ukraine as part of its war on Kyiv. Iran has issued a series of conflicting denials about its drones being used in the war, though Western nations and experts have tied components in the drones back to Tehran.
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. Michael "Erik" Kurilla, the head of the American military's Central Command, warned that American 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.
Addressing the U.S. House Armed Services Committee on Thursday, Kurilla warned lawmakers 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.
Kurilla also alleged that Iran had launched some 78 attacks on U.S. positions in Syria since January 2021.
"What Iran does to hide its hand is they use Iranian proxies," Kurilla said.
Diplomacy to deescalate the crisis appeared to begin immediately around the strikes. Qatar's state-run news agency reported a call between its foreign minister and Jake Sullivan, the U.S. national security adviser. Doha has been an interlocutor between Iran and the U.S. recently amid tensions over Tehran's nuclear program.
Qatar's foreign minister also spoke around the same time with Iranian Foreign Minister Hossein Amirabdollahian.
Austin said he authorized the retaliatory strikes at the direction of President Joe Biden.
"As President Biden has made clear, we will take all necessary measures to defend our people and will always respond at a time and place of our choosing," Austin said. "No group will strike our troops with impunity."
The U.S. under Biden has struck Syria previously over tensions with Iran. In February and June of 2021, as well as August 2022, Biden launched attacks there.
U.S. forces entered Syria in 2015, backing allied forces in their fight against the Islamic State group. The U.S. still maintains the base near Hasakah in northeast Syria where Thursday's drone strike happened. There are roughly 900 U.S. troops, and even more contractors, in Syria, including in the north and farther south and east.
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. "Due to the geographical proximity, Iraqi groups also intensified their activities in the border strip with Syria and in the Deir el-Zour province."
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.