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Seven soldiers and a civilian were killed in air strikes in Syria's Deir Ezzor province at dawn on Tuesday, which a Syrian military source blamed on the US, although Washington has denied involvement.
The strikes were the first to hit eastern Syria since early February and came hours after an Iranian plane reportedly carrying weapons and IRGC members landed at Deir Ezzor airport, the Syrian Observatory for Human Rights said.
Syrian media said the strikes were carried out by the US and injured 32 people, including civilians.
Deputy Pentagon press secretary Sabrina Singh said that the US "did not conduct strikes in Syria last night".
The Israeli military has not yet commented.
The attacks hit "a number of villages, towns and military sites in Deir Ezzor province and its countryside", the military source was reported by Syrian official media as saying.
The attack also caused damage to public and private property, the source added.
Earlier in the day, local sources told The National that at least six people had been killed and about 20 injured in air strikes in Deir Ezzor province.
Strikes hit sites including Deir Ezzor city and Al Suwayiyah, a town in the province. Abu Kamal, on the Iraq-Syria border, was also hit.
A Syrian source in Deir Ezzor reported that several aircraft carried out 10 strikes at about 1am.
The sources said the strikes resulted in several deaths and injuries, among them civilians.
The Syrian Observatory for Human Rights and local news service DeirEzzor24, both linked to the Syrian opposition, claimed the bombings hit the headquarters of a militia allied with Iran's Islamic Revolutionary Guard Corps.
The observatory claimed some members of the IRGC, stationed in Syria to advise government forces and allied militias, were among the dead.
“Unidentified aircraft, whether Israeli or American, carried out raids on Iranian militia positions in Deir Ezzor governorate, resulting in deaths and injuries,” it said.
The strikes came hours after an Iranian plane carrying weapons and IRGC members landed at Deir Ezzor airport, it added.
DeirEzzor24 reported that the wounded included senior IRGC commander Hajj Askar.
Damascus-based Syrian analyst Kamal Al Jafa said reports that the IRGC was hit in the strikes were "inaccurate because the building had been previously evacuated".
"Although one of the air strikes targeted the former headquarters of Hajj Askar near Al Maarri School in the city, but it was empty and had been evacuated a some time ago," Mr Al Jafa said.
Mr Askar oversaw the confiscation of Syrian farmland and properties in the area, along with another IRGC commander, Hajj Mahdi, according to the Washington Institute for Near East Policy, a think tank.
Iran has sought to maintain a strong presence in border areas with Iraq, particularly Abu Kamal and Al Qaim, towns on the Syrian and Iraqi side of the border, respectively, with the aim of controlling key overland routes for moving weapons into Syria.
Israel has struck Syria several times since the Gaza war began, hitting Iranian military positions and Tehran-backed groups across the country, including the capital, Damascus.
In January, an Israeli air strike in Damascus killed the head of Iranian intelligence in Syria, an attack that was condemned by Iran’s President Ebrahim Raisi as a “cowardly assassination”.
The previous month, another Israeli strike killed Razi Mousavi, a senior member of the IRGC responsible for co-ordinating Syrian and Iranian military activities.
Tuesday’s strikes were the first in this part of Syria since early February, the observatory said.
US strikes in the cities of Deir Ezzor and Al Madayeen in early February killed 29 pro-Iran fighters in response to a deadly drone attack on an American base in Jordan, which killed three soldiers.