The US military struck Iran-backed militias in eastern Syria in what the Pentagon said was a message from the new administration after recent rocket attacks targeting US troops in Iraq.

In its first military action against Iran-linked groups since Joe Biden became US president five weeks ago, the Pentagon said it had carried out airstrikes on Thursday at a Syria-Iraq border control point used by Iran-backed groups, destroying "multiple facilities".

"At President Biden's direction", the US raids targeted "infrastructure utilized by Iranian-backed militant groups in eastern Syria," spokesman John Kirby said in a statement.

"These strikes were authorized in response to recent attacks against American and coalition personnel in Iraq, and to ongoing threats to those personnel," he said.

The strikes destroyed multiple facilities located at a border control point used by a number of Iranian-backed militant groups. The Syrian Observatory for Human Rights, a war monitor, said at least 22 fighters were killed when the strike hit three trucks loaded with munitions coming from Iraq near the Syrian border town of Albu Kamal.

Hours after the strike, Iran's Foreign Minister Mohammad Javad Zarif on Friday spoke to his Syrian counterpart, saying "the two sides stressed the need of the West to adhere to the United Nations Security Council resolutions regarding Syria".

Chinese Foreign Ministry spokesman Wang Wenbin on Friday called on all parties concerned to respect Syria's sovereignty, independence and territorial integrity, and avoid adding new complications to the situation in Syria.

Recent rocket attacks

On Monday, two rockets landed in the heavily fortified Green Zone in the center of the Iraqi capital Baghdad. The attack caused no casualties and was claimed by none.

On Feb 15, a rocket strike targeted coalition forces near the Erbil International Airport in the semi-autonomous region of Kurdistan in northern Iraq, which houses a US-led coalition military base.

Under such circumstances, the latest strike should be viewed as a "retaliatory response", said Li Shaoxian, a Middle East studies expert at Ningxia University.

"The signal released this time is to warn the Iran-backed militants to restrain themselves, and the US military cannot tolerate what they have done," Li said.

Unlike what the US has done in Syria before, Li said this time the US military acted "very low-key" as the United States did not comment publicly on the military operation and the force deployed was also very limited.

However, some believe the airstrike was a sign the US is changing its Middle East policy, as it was different from what Biden's predecessor Donald Trump used to do.

The military operation was against facilities in Syria, but clearly it was aimed at Iran, said Yin Gang, a researcher from the Institute of West-Asian and African Studies of the Chinese Academy of Social Sciences.

"It can be seen as a reversal of Trump's previous policies to sanction Iran with economic measures," he said.

Thursday's airstrike also came at a time when the Biden administration said it was ready to engage in negotiations with Iran over the nuclear issue.