UPDATE 4-US strikes Iran-backed facilities in Syria after drone kills American
American contractor killed, six wounded in drone attack
Rights group says eight pro-Iran fighters killed in US strikes
Iran TV says no Iranian killed
Retaliatory strikes carried under direction of President Biden
(Updates March 23 story on March 24 to add comments by Iran's Press TV, in paragraphs 11-12)
By Phil Stewart and Idrees Ali
WASHINGTON, March 23 (Reuters) - The U.S. military carried out multiple air strikes in Syria on Thursday night against Iran-aligned groups that it blamed for a drone attack that killed an American contractor, wounded another and also hurt five U.S. troops, the Pentagon said.
Both the attack on U.S. personnel and the retaliation were disclosed by the Pentagon at the same time late on Thursday.
The attack against U.S. personnel took place at a coalition base near Hasakah in northeast Syria at approximately 1:38 p.m. (1038 GMT) on Thursday, it said.
The U.S. intelligence community assessed that the one-way attack drone was Iranian in origin, the military said, a conclusion that could further aggravate already strained relations between Washington and Tehran.
Although U.S. forces stationed in Syria have been targeted by drones before, fatalities are extremely rare.
U.S. Defense Secretary Lloyd Austin said the retaliatory strikes were carried out at the direction of President Joe Biden and targeted facilities used by groups affiliated with Iran's Islamic Revolutionary Guards Corps (IRGC).
"The air strikes 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 IRGC," Austin said in a statement.
"No group will strike our troops with impunity."
The Syrian Observatory for Human Rights, a group that monitors the war in Syria, said the U.S. strikes had left eight pro-Iranian fighters dead in Syria.
Reuters was unable to independently confirm the toll.
Iran's state Press TV, saying no Iranian had been killed in the attack, quoted local sources as denying the target was an Iran-aligned military post, but that a rural development center and a grain center near a military airport were hit.
It said: "A military source in Syria told Press TV that the resistance groups reserve their right to respond to the American attack and will take reciprocal action."
The drone attack on U.S. personnel caused wounds that, for three services members and a contractor, required medical evacuation to Iraq, where the U.S.-led coalition battling the remnants of Islamic State has medical facilities, the Pentagon said. The other two wounded American troops were treated at the base in northeast Syria, it added.
U.S. troops have come under attack by Iranian-backed groups about 78 times since the beginning of 2021, according to Army General Erik Kurilla, who oversees U.S. troops in the Middle East as the head of Central Command.
Deployments in Iraq, where Iran also holds sway, have also come under drone and rocket attacks in recent years.
Kurilla, testifying to the House Armed Services Committee earlier on Thursday, cautioned about Iran's fleet of drones.
"The Iranian regime now holds the largest and most capable unmanned aerial vehicle force in the region," he said.
Three drones targeted a U.S. base in January in Syria's Al-Tanf region. The U.S. military said two of the drones were shot down while the remaining drone hit the compound, injuring two members of the Syrian Free Army forces.
U.S. officials believe drone and rocket attacks are being directed by Iran-backed militia, a reminder of the complex geopolitics of Syria where President Bashar al-Assad counts on support from Iran and Russia and sees U.S. troops as occupiers.
The attack came just weeks after the top U.S. general, Mark Milley, visited northeast Syria to assess the mission against Islamic State and the risk to U.S. personnel.
Asked by reporters traveling with him if he believed the deployment of roughly 900 U.S. troops to Syria was worth the risk, Milley tied the mission to the security of the United States and its allies, saying: "If you think that that's important, then the answer is 'Yes.'"
"I happen to think that's important," Milley said.
The U.S. deployment, which former President Donald Trump nearly ended in 2018 before softening his withdrawal plans, is a remnant of the larger global war against terrorism that had included once the war in Afghanistan and a far larger U.S. military deployment to Iraq.
While Islamic State has lost the swathes of Syria and Iraq it ruled over in 2014, sleeper cells still carry out hit-and-run attacks in desolate areas where neither the U.S.-led coalition nor the Syrian army exert full control.
Thousands of other Islamic State fighters have been detained by the Kurdish-led Syrian Democratic Forces, America's key ally in the country. American officials say Islamic State could still regenerate into a major threat. (Reporting by Phil Stewart, Idrees Ali, Akriti Sharma and Dan Whitcomb; Editing by Christian Schmollinger, Raju Gopalakrishnan and Himani Sarkar)