DAMASCUS, Oct. 22 (Xinhua) -- The U.S.-backed Syrian Democratic Forces (SDF) advanced on Monday into the last Islamic State (IS)-held pocket in the eastern province of Deir al-Zour, a war monitor reported.

The move was part of a wide-scale offensive launched last month to eradicate the terror-designated group in the key area near the Iraqi border, said the Syrian Observatory for Human Rights.

The Kurdish-led SDF, backed by the U.S.-led coalition, captured on Monday parts of the town of Souseh on the eastern bank of Euphrates River in eastern Deir al-Zour countryside.

On Saturday, State news agency SANA said U.S.-led strikes killed 63 civilians within 24 hours in the eastern countryside of Deir al-Zour.

The SDF launched a wide-scale offensive on the last IS-held pocket on the eastern bank of the Euphrates River in eastern Deir al-Zour on Sept. 10.

The IS militants attempted to thwart the SDF advance through mines, some of which are advanced and laser-controlled and difficult to be detected.

The terror group also carried out suicide bombings to stop the SDF from advancing in the areas of Baghous and Hajin in the last IS-held pocket in the eastern countryside of Deir al-Zour.

Recent reports said the IS-controlled Syrian territory has shrunk to one percent from almost half of the country a couple of years ago.

The Syrian army has cleared IS militants from large swathes of areas in Deir al-Zour, while the SDF is attempting to consolidate positions in the strategic oil-rich northern and northeastern countryside of the province near the Iraqi border.