DAMASCUS, June 18 (Xinhua) -- At least 40 pro-Syrian government fighters were killed by foreign airstrikes that targeted Syrian military positions in the east of the country a day earlier, a monitor group reported Monday.

The targeted sites reportedly belong to the Lebanese Hezbollah group and other pro-government forces near the Syrian-Iraqi border in the southeastern countryside of Deir al-Zour Province.

The London-based Syrian Observatory for Human Rights said the identity of the warplanes are unknown, adding that the death toll is likely to rise, as many fighters are either in critical conditions or missing.

On the other hand, the Syrian state TV said late on Sunday that the attack was carried out by the U.S.-led coalition.

It said the airstrikes targeted the Syrian military sites in the town of Hiry, southeast of the city of al-Bukamal in the countryside of Deir al-Zour.

It added that the strike caused casualties, without revealing the number of deaths or the identity of victims.

The strike is not the first suspected U.S.-led attack targeting Syrian military positions in Deir al-Zour.

In May, 12 pro-government fighters were killed by suspected U.S. strikes on Syrian positions in Deir al-Zour, according to the Observatory.

The recent strike comes as the Islamic State (IS) militant group is reportedly preparing to launch an offensive on Syrian military sites in the eastern countryside of Deir al-Zour.

The Syrian government has for long accused the U.S.-led coalition of rendering support to IS militants in Deir al-Zour, where the terror-designated group is in control of some pockets.