DAMASCUS, May 24 (Xinhua) -- At least 12 pro-Syrian government fighters were killed in the U.S.-led airstrikes that targeted Syrian military positions in eastern Syria on Thursday, a monitor group reported.

The slain fighters were non-Syrians, and the strikes are believed to have been carried out by the U.S.-led coalition against the military sites in the countryside of the eastern province of Deir al-Zour, said the Syrian Observatory for Human Rights.

Earlier Wednesday, state news agency SANA said the Syrian army responded to an attack by IS in the southern countryside of Deir al-Zour.

Meanwhile, the War Media, the media wing of the Syrian army and its Iranian allies, said two Syrian military positions were hit by the U.S.-led airstrikes in the vicinity of the T-2 oil station in the desert region south of Deir al-Zour.

The attack came as activists reported shelling between the Syrian army and the U.S.-backed Syrian Democratic Forces (SDF) in the countryside of Deir al-Zour earlier on Wednesday.

Such skirmishes reflect the tension between the Syrian army and the U.S.-backed fighters in Deir al-Zour, a key oil-rich province the United States is eyeing to have a sway at.

The United States and Israel have struck several Syrian military positions recently, targeting areas where Iranian military experts are located.

Syrian President Bashar al-Assad said Wednesday that some international parties, referring to the West, which are "separated from reality when it comes to approaching the situation in Syria, are an obstacle to any breakthrough in the political track."

He further urged such powers to show a minimum amount of political realism, halt the support for terrorism and embrace political work.

His remarks were made during his meeting with the visiting Russian President's Special Envoy on Syria Alexander Lavrentiev.

The attack Thursday comes as Syria's Deputy Foreign Minister Faisal Mekdad told Russia's Sputnik that the withdrawal of Iran and the Lebanese Hezbollah group from Syria is not on the discussion agenda, as those forces have come to Syria upon the invitation of the government.