A dozen fighters have been killed in overnight air strikes against Syrian military sites that a war monitor blamed on U.S.-led coalition jets, though the Pentagon denied the report.
Syrian officials said the bombardment struck bases manned by Iran's Islamic Revolutionary Guards Corps, but they said that Iranian and allied Hezbollah fighters were not among the dead.
The Syrian Observatory for Human Rights, a war monitor based in Britain, said the dead also did not include Syrian government troops, but described them as pro-government fighters, which could include Iraqi Shi'ite militias.
Syrian state news agency SANA said that several military posts located between the Syrian desert and the Iraqi border were hit by U.S.-led air strikes, resulting in only material damage.
But Pentagon spokesman Lieutenant Colonel Kone Faulkner said: "These reports are false. The coalition did not strike any Syrian Army positions in eastern Syria."
Later on May 24, air strikes hit the Al-Daba air base southwest of Homs, the monitoring group and activists said.
Activists said fighters from Hezbollah were gathered on the base at the time of the attack.
The base is about 10 kilometers from Lebanon's border, and the roar of the jets overhead could be heard in areas around Beirut.
Although it was not known who carried out the air strikes, Israel has launched similar strikes in the past on Syrian military targets which also serve as bases for Hezbollah fighters and Iran's Revolutionary Guards.
Hezbollah and Iran have increased their military presence in Syria in recent years, playing a key role in gains made by the government in its seven-year civil war against Sunni rebels.
Israeli leaders have said they won't accept a permanent Iranian military presence in Syria.