The US military has launched air strikes against targets in Syria in the first retaliation for a drone attack that killed three soldiers at a remote US base in Jordan, US media reported Friday.

The Pentagon did not immediately comment on the reports. Fox News cited an unidentified Defence Department official saying the strikes were launched from multiple platforms.

Another report -- from the Syrian Observatory for Human Rights war monitor -- said that six members of a pro-Iran militia group had been killed in eastern Syria during strikes believed to be carried out by the United States.

Warplanes carried out four rounds of raids on sites housing Iran-backed groups in the eastern Deir Ezzor province, the Observatory said, three of them targeting al-Mayadeen and one striking Albu Kamal, near the Iraqi border.

The reported start of US bombing in the region follows President Joe Biden's vow to retaliate against pro-Iranian militias over the drone attack last Sunday against a US base in Jordan, near Syria. (AFP)