The Syrian Observatory for Human Rights said "19 pro-Iranian fighters, including four Syrians, and six Iraqis, were killed and more than 18 were wounded" in at least nine air strikes overnight near the Iraqi border.

It said the raids were "likely carried out by Israel", after earlier indicating they were "likely American".

A US military official, requesting anonymity, said the "US did not conduct any defensive strikes overnight".

The Observatory said the strikes targeted military positions in Albu Kamal and its surroundings in Deir Ezzor province, adding that a weapons shipment from Iraq and an ammunition warehouse were also hit.

Israel rarely comments on individual strikes targeting Syria, but it has repeatedly said it will not allow arch-foe Iran, which backs President Bashar al-Assad's government, to expand its presence there.

Later Saturday, the Observatory said that "Israeli missiles targeted warehouses and bases of pro-Iran groups" in northern Syria in an area near the Aleppo airport, killing three fighters and wounding several others.

Syrian state media, citing a military source, said that at around 5:20 pm (1420 GMT), "the Israeli enemy carried out an air attack... targeting a number of points south of the city of Aleppo", reporting only "material damage".

During more than a decade of civil war in Syria, Israel has launched hundreds of air strikes on its territory, primarily targeting Iran-backed forces including Lebanese Hezbollah fighters as well as Syrian army positions.

But it has intensified attacks since the war between Israel and Hamas began on October 7, as tensions rise across the Middle East.

Iranian state media said an Israeli strike on Monday near Damascus killed Razi Moussavi, a senior commander in the Quds Force, the foreign operations arm of Iran's Islamic Revolutionary Guard Corps.

- Strikes in south Syria -

Overnight in southern Syria's Quneitra province, near the Israeli-occupied Golan Heights, "Israeli ground bombardment" killed two fighters from a Hezbollah-linked group, said the Britain-based Observatory.

The pair, "of Palestinian origin", were "members of a group affiliated with the Syrian Resistance to Liberate the Golan, which works with Lebanon's Hezbollah", said the monitor which relies on sources inside war-torn Syria for its reports.

The Israeli army had said early Saturday that it was carrying out strikes in Syria after two rockets fired from the country fell into territory under its control.

The army did not give the precise location where they fell.

Lebanon's powerful Hezbollah movement, which like Hamas in the Gaza Strip is supported by Iran, announced on Saturday the death of four of its fighters "on the road to Jerusalem" -- a reference to militants killed in hostilities since October 7.

It was unclear where they were killed.

There have been regular cross-border exchanges of fire between Israel and Hezbollah in southern Lebanon.

The Middle East has also seen a surge in attacks on US forces, which Washington blames on Tehran-aligned armed groups across the region, since the start of the Israel-Hamas war.

The majority have been claimed by the Islamic Resistance in Iraq, a loose formation of Iran-linked armed groups which oppose US support for Israel.