The Pentagon did not immediately comment on the reports. Fox News cited an unidentified Defense 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.

Just minutes before the first US media reports, Biden had attended a solemn military ritual at a Delaware air base for the return of the three dead soldiers.

Six servicemen wearing camouflage, dark berets and white gloves marched slowly three times on and off the ramp of a huge C-5 transport plane to carry the bodies in flag-draped "transfer cases" -- as the military calls caskets used in transportation -- to a waiting van.

Biden, accompanied by First Lady Jill Biden, watched with his hand over his heart and a grim expression. Family members watched from their own area, screened off from the press.

Other than the terse military commands to the pallbearers, there was total silence across the vast airfield, emphasizing the powerful -- but restrained -- emotion of the day.

The secretary of defense, Lloyd Austin, and the chairman of the Joint Chiefs of Staff, CQ Brown, also attended what's known as a "dignified transfer" -- their presence highlighting the importance, as well as relative rarity, of returning dead service members in the wake of US exits from major foreign conflicts.

William Rivers, Kennedy Sanders and Breonna Moffett, all from the southern state of Georgia, were killed in a drone strike. The White House blames the Islamic Resistance in Iraq militia for the attack.

Although the United States is now free from its wars in Iraq and Afghanistan, surging tensions in the Middle East, sparked by the Israel-Hamas fighting, threaten to drag US forces back into regional conflict.

These were the first US military deaths to hostile fire since the October 7 Hamas surprise attack on Israel that sparked a deadly Israeli assault on Gaza.

However, the US military and Iran-backed groups in Iraq and Syria have periodically exchanged fire, while Yemen's Huthi rebels are near daily clashing with the US Navy ships or firing on international civilian shipping in the Red Sea.

Two SEALS -- among the most elite special forces in the US military-- died while trying to board and search a ship in January.

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