WASHINGTON, Sept. 11 (Xinhua) -- The U.S.-backed Syrian Democratic Forces (SDF) has kicked off the final phase of its campaign against the Islamic State (IS) militants, said the Pentagon on Tuesday.

The SDF, with the help of the U.S.-led coalition, initiated ground operations for Phase Three of Operation Roundup on Monday, aiming to clear the remaining IS forces in Iraq and Syria from northeastern Syria, said the Pentagon in a statement.

The U.S.-led military actions started in September 2014 were condemned by the Syrian government as an intervention to the country's internal affairs. The Bashar Assad administration has for long blamed Washington and its Mid-East allies for the deaths of Syrian civilians during unauthorized operations.

The operations were widely seen as part of the U.S. attempts to secure its influence and benefits in the oil-rich region.

According to the Syrian Observatory for Human Rights on Tuesday, the SDF is advancing in the last IS-held pocket on the eastern bank of the Euphrates River in the eastern countryside of Deir al-Zour, following 24 hours of the beginning of the wide-scale assault in that area.?