BEIRUT (AFP) - A US-backed Arab-Kurdish alliance advanced Wednesday (Dec 21) to several kilometres from the largest prison held by the Islamic State jihadist group in Syria's northern province of Raqa, a monitor said.

Members of the Syrian Democratic Forces (SDF) were eight kilometres from the jail near the country's largest dam at Tabqa on the Euphrates River, the Syrian Observatory for Human Rights said.

On Dec 10, the SDF announced "phase two" of its campaign against ISIS's de facto Syrian capital of Raqa some 50 kilometres east of Tabqa in the same province.

The alliance has since captured dozens of villages and hamlets, the Observatory says, after taking 700 square kilometres from the jihadists in a first phase of the assault from Nov 5.

Western hostages of the jihadist group are believed to have been held at the jail near the town of Taqba, where top ISIS leaders live, the Britain-based Observatory said.

The SDF is backed by air strikes from a US-led coalition as well as by some US forces on the ground.

Washington said this month it was sending 200 additional troops to join the 300 it has already deployed to support the Raqa campaign.

Despite recent setbacks, ISIS still controls areas of Syria and neighbouring Iraq, where it has faced an offensive since October on its main bastion of Mosul.

This month, ISIS seized the ancient city of Palmyra in central Syria for the second time, just eights months after President Bashar al-Assad's army backed by Russia drove the jihadists out.

ISIS overran large parts of Syria and Iraq in 2014, proclaiming Raqa the capital of its "caliphate", after Syria's war started in 2011 with the brutal repression of anti-government protests.</s>A U.S.-backed Arab-Kurdish alliance advanced Wednesday to several kilometers from the largest prison held by the Islamic State jihadist group in Syria's northern province of Raqa, a monitor said.

Members of the Syrian Democratic Forces (SDF) were eight kilometers (five miles) from the jail near the country's largest dam at Tabqa on the Euphrates River, the Syrian Observatory for Human Rights said.

On December 10, the SDF announced "phase two" of its campaign against IS' de facto Syrian capital of Raqa some 50 kilometers east of Tabqa in the same province.

The alliance has since captured dozens of villages and hamlets, the Observatory says, after taking 700 square kilometers (270 square miles) from the jihadists in a first phase of the assault from November 5.

Western hostages of the jihadist group are believed to have been held at the jail near the town of Tabqa, where top IS leaders live, the Britain-based Observatory said.

Kurdish officials told AFP on Wednesday that many of the jihadists had fled before the SDF advance.

IS fighters "have no more heavy weapons -- they are weakened and flee without resisting," said Moslem Sheikh Nouh, a commander with the alliance.

"IS is not resisting, absolutely not," she said, adding that the jihadists "take to their heels in flight."

The SDF is backed by air strikes from a U.S.-led coalition as well as by some U.S. forces on the ground.

Washington said this month it was sending 200 additional troops to join the 300 it has already deployed to support the Raqa campaign.

Despite recent setbacks, IS still controls areas of Syria and neighboring Iraq, where it has faced an offensive since October on its main bastion of Mosul.

This month, IS seized the ancient city of Palmyra in central Syria for the second time, just eights months after President Bashar Assad's army backed by Russia drove the jihadists out.

IS overran large parts of Syria and Iraq in 2014, proclaiming Raqa the capital of its "caliphate", after Syria's war started in 2011 with the brutal repression of anti-government protests.
U.S.-backed Syrian Democratic Forces advance to eight kilometers (five miles) from the largest prison held by ISIL near the Tabqa Dam.