BEIRUT -- Iran-backed fighters were on alert in eastern Syria on Saturday, a day after U.S. forces launched retaliatory airstrikes on sites in the war-torn country, opposition activists said.
The airstrikes came after an attack Thursday by a drone hit a coalition base in the northeast Syrian city of Hasakeh, and killed a U.S. contractor and wounded five American service members and one contractor.
The American intelligence community determined the drone in Thursdays attack was of Iranian origin, Defense Secretary Lloyd Austin said, but offered no other immediate evidence to support the claim.
In the first Syrian comment since the attacks occurred, the foreign ministry condemned the U.S. strikes saying they are "a flagrant violation of Syria's sovereignty." The ministry added in a statement that Damascus aims to end "American occupation" and spread government control over all parts of the country.
President Joe Biden said Friday 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.
"The United States does not, does not seek conflict with Iran," Biden said in Ottawa, Canada, where he was 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. Thats exactly what happened last night."
Activists said the U.S. bombing killed at least four people.
In Iran, domestic media outlets quoted a spokesman for the nation's Supreme National Security Council, Keivan Khosravi, as saying that Tehran would immediately respond to any U.S. attack on Iranian bases in Syria.
"Any excuses-seeking attitude for attack on bases that are established at the request of the Syrian government, will immediately face an answer," Khosravi was quoted as saying. Khosravi rejected U.S charges that Iran is behind attacks on American bases in Syria, suggesting they are attacks against "illegal occupation of part of Syria."
A statement issued late Friday by the Iranian Consultative Center in Syria warned the U.S. not to carry out further strikes in Syria. Otherwise, "we will have to retaliate." It warned that "it will not be a simple revenge."
The center said the strike killed seven people and wounded seven others without giving the nationalities of the dead. An official with an Iran-backed group in Iraq said the strikes killed seven Iranians.
The Syrian Observatory for Human Rights, an opposition war monitor, raised the death toll from the U.S. strikes to 19, reporting that they were killed in an arms depot in the city of Deir el-Zour, and two military posts near the towns of Mayadeen and Boukamal.
Iran-backed militia groups and Syrian forces control the area.
According to U.S. officials, two simultaneous attacks were launched at U.S. forces in Syria late Friday.
Based on preliminary information, officials said there was a rocket attack on the Conoco plant, where U.S. troops are stationed, and one U.S. service member was wounded but is in stable condition. At about the same time, several drones were launched at Green Village, in Deir el-Zour province 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.
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 others countries.
The State Department said Saturday in a statement they have been in contact with Saudi officials about their approach to the region, including with Syria adding that Washingtons stance against normalization with Assad's government "remains unchanged, and we have been clear about this."
The State Department said the U.S.' consistent message to regional partners who are engaging with the Syrian government has been that "credible steps to improve the situation for the Syrian people should be front and center in any engagement."
Information for this article was contributed by Nasser Karimi, Jon Gambrell and Albert Aji of The Associated Press.