BEIRUT (Reuters) -Strikes on Iranian-linked bases in Syria would draw a quick response, an Iranian security spokesperson said on Saturday, after the reported death of 19 people in one of the deadliest exchanges between the U.S. and Iranian-aligned forces in years.
"Any pretext to attack bases created at the request of the Syrian government to deal with terrorism and Islamic State elements in this country will be met with an immediate counter-response," Keyvan Khosravi, spokesperson for Iran's top security body, was quoted as saying by Iranian state media.
Iran says its forces and allied fighters are in Syria at the request of Damascus, and sees U.S. forces there as occupiers.
The death toll in U.S. air strikes on pro-Iran installations in eastern Syria has risen to 19 fighters, a Syrian war monitoring group said on Saturday.
The U.S. carried out strikes in eastern Syria in response to a drone attack on Thursday that left one American contractor dead and another wounded along with five U.S. troops. Washington said the attack was of Iranian origin.
The U.K.-based Syrian Observatory for Human Rights said air raids killed three Syrian troops, 11 Syrian fighters in pro-government militias and five non-Syrian fighters who were aligned with the government.
The monitoring group's head Rami Abdel Rahman could not specify the nationalities of the foreigners. Reuters was unable to independently confirm the toll.
The initial exchange prompted a string of tit-for-tat strikes. Another U.S. service member was wounded, according to officials, and local sources said suspected U.S. rocket fire hit more locations in eastern Syria.
President Joe Biden on Friday warned Iran that the United States would "act forcefully" to protect Americans.
Iran has been a major backer of President Bashar al-Assad during Syria's 12-year conflict.
Iran's proxy militias, including the Lebanese group Hezbollah and pro-Tehran Iraqi groups, hold sway in swathes of eastern, southern and northern Syria and in suburbs around the capital.
Iran's foreign ministry condemned the latest U.S. strikes, accusing U.S. forces of targeting "civilian sites".
"Iran's military advisers have been in Syria at the request of the Syrian government to help this country fight terrorism, and shall remain by Syria's side to help establish peace, stability and lasting security," ministry spokesperson Nasser Kanaani told state media.
Tehran's growing entrenchment in Syria has drawn regular Israeli air strikes but American aerial raids are more rare. The U.S. has been raising the alarm about Iran's drone program.