Syrian troops battling IS advance toward US-backed force

Syrian troops battling the Islamic State group crossed to the eastern bank of the Euphrates River in Deir el-Zour on Monday, threatening a potential standoff with the U.S.-backed forces operating there.

The crossing came nearly two weeks after the Russia-backed Syrian troops breached a three-year siege on their troops in the city. It tightens the government's grip on the eastern city by closing in on the militants from all sides, except for a narrow waterway flowing south.

The pro-government forces meanwhile announced that they had secured the airport in Deir el-Zour, allowing two military transport aircraft to land. Al-Manar TV, the media arm of Lebanon's Hezbollah, quoted an unnamed general who said the airport is "90 percent secured." Hezbollah is fighting alongside President Bashar Assad's forces.

Deir el-Zour is one the militants' last major urban stronghold in Syria and is home to nearly 100,000 residents. IS militants still have pockets inside the city on the western and eastern banks of the river.

Russia, which has provided crucial air support to Assad's forces, announced the crossing of the river, saying in a statement that the troops used a pontoon bridge, as well as Syrian elite troops.

"The Syrian army storm units have pushed the IS militants out of several villages on the eastern bank of the Euphrates River and are continuing their offensive toward the east, extending their gains."

Rami Abdurrahman, the head of the Britain-based Syrian Observatory for Human Rights, confirmed the crossing, which he said was preceded by intense aerial bombing on the eastern bank. He said the government forces are now in Marrat, battling IS militants in Hatlah to the north.

"Even if the pro-government (forces) keep up their advance in the city, it will mean nothing if they don't control the eastern bank," Abdurrahman said.

The new government push brings them only miles away from the U.S.-backed and Kurdish-led forces, which have also been advancing on the eastern side of the river. Both sides are seeking to expand their control of the oil-rich province bordering Iraq. Many oil fields, including al-Omar, Syria's largest, are scattered on the eastern bank. The new move raises concerns over potential friction.

Over the weekend, the U.S.-backed Syrian Democratic Forces said its fighters were hit by Russian airstrikes on the eastern bank of the river, in an industrial area they recently liberated from IS. Russia denied it was behind the airstrikes.

On Monday, SDF spokesman in Deir el-Zour, Bassem Aziz, said only miles of IS-controlled territory separated them from government forces on the eastern bank. He said his forces will avoid any clashes as SDF commanders convened to review their plans. Aziz said the eastern banks of the Euphrates river remain the focus of their advances.

The U.S.-backed offensive is focused on the Iraq border area, which is still controlled by IS. Washington fears that further advances by pro-government forces in Syria could help Iran expand its influence across the region via a land bridge stretching through Iraq, Syria and Lebanon, all the way to Israel.

Iran is a key ally of Assad, and has provided financial and logistical support to his forces throughout the six-year civil war.

The town of al-Mayadeen, south along the river, has become the main hub for IS leadership as the group's strongholds of Raqqa and Deir el-Zour have come under attack. Further south, Boukamal sits on the border between Iraq and Syria and would be crucial in any future plans to control the route between the two countries.