Air strikes in eastern Syria on Tuesday killed at least 15 people, most of them pro-Iran fighters including an Iranian Revolutionary Guard, a war monitor said, with Iranian media confirming the guard's death.

The Syrian Observatory for Human Rights did not say who carried out the strikes in Deir Ezzor province, which has been targeted by both US and Israeli raids in the past.

A US defence official told AFP the United States "did not conduct any airstrikes" overnight.

The Observatory said that "an Iranian Revolutionary Guards adviser, his two Iranian security escorts, two Syrian fighters" and five other combatants belonging to pro-Iran groups were killed in a villa in Deir Ezzor city.

Iran's state news agency IRNA reported the attack was "carried out by the Zionist regime", its term for Israel.

It identified the dead guard as Behrouz Vahedi, saying he belonged to the Quds force, the foreign operations arm of Iran's Islamic Revolutionary Guard Corps.

The Observatory said the villa "served as a communications centre" in the area, reporting that the building was destroyed and its Syrian owner, a civilian, was also killed.

Four other fighters were killed in a separate strike in the town of Albu Kamal on the Iraqi border, said the Britain-based Observatory, which has a network of sources inside Syria.

It said in total nine of the dead in the strikes were Iraqi nationals.

Israel has carried out hundreds of strikes targeting pro-Iranian groups fighting alongside the forces of President Bashar al-Assad in the country's 13-year civil war.

The US has carried out fewer strikes in eastern Syria against pro-Iran groups, which it blames for a flurry of attacks on US interests in Iraq and Syria during the Israel-Hamas war in Gaza.

  'Windows shattered' 

 Hammoud al-Jabbour, who lives a short walk from the villa, told AFP he was woken up by the sound of explosions.

"It was one of the biggest strikes I've heard," he said.

"The windows of my house were shattered, the power was cut in several neighbourhoods and the main roads were closed."

The Observatory said an Iranian cargo plane flew from Damascus to Deir Ezzor city shortly before the strike, carrying technical equipment and the Guards adviser.

The Observatory said he was in charge of telecommunications.

The strikes were the first of their kind in eastern Syria since early February, the Observatory said.

US strikes in February killed 29 pro-Iran fighters in Deir Ezzor and Mayadeen areas in response to a deadly drone attack on a US base that killed three US soldiers across the border in Jordan.

Pro-Iran groups have since cut back their attacks on US targets in Syria, the Observatory said.

In early March, an Iranian Revolutionary Guard was killed along with two other people in an Israeli strike on the Syrian Mediterranean city of Banias.