DAMASCUS, Jan. 27 (Xinhua) -- Four Islamic State (IS) suicide bombers detonated themselves during a counter-offensive against the Kurdish-led Syrian Democratic Forces (SDF) overnight in eastern Syria, a war monitor reported Sunday.

The four bombers in four car bombs targeted the SDF in the eastern countryside of Deir al-Zour province, where the final stage of battles is taking place between the IS and the SDF.

The Syrian Observatory for Human Rights said the bombings are part of clashes that took place overnight as the SDF is trying to completely defeat IS while the later is fighting for its last positions in that part of the country.

The overnight battles and bombings led to the killing of 19 IS militants in addition to the four bombers and 11 SDF fighters, said the UK-based watchdog group.

The fighting comes as the IS group has lost all villages and towns in the eastern Euphrates region and is now controlling a few farms in that area.

The Observatory said that around 1,250 IS militants have been killed since the SDF, with the backing of the U.S.-led coalition, launched a wide-scale offensive to defeat IS in the eastern Euphrates region last September.