Syrian Arab, Kurdish, and Christian fighters appeared to have seized a strategic dam in northern Syria, as the air-strike death of another rebel commander near Damascus injected new uncertainty into peace talks set for next month.
Colonel Talal Selo, a spokesman for the coalition known as Democratic Syria, said its fighters has captured the Tishrin Dam, on the Euphrates River, from Islamic State militants on December 26.
The Syrian Observatory for Human Rights, a British-based monitoring group, also said the coalition was engaged in fierce battles against Islamic State fighters after taking the dam.
The move was part of its offensive aimed at cutting supply lines between Islamic State strongholds in northern Syria, which gets much of its electricity from the dam.
The coalition, which is backed by the United States, is aiming to uproot Islamic State fighters from their stronghold in Raqqa, about 22 kilometers down river.
Another coalition spokesman said earlier this week that the forces were also trying to cut the supply lines between Raqqa and another town, Manbij, northwest of the dam.
Meanwhile, the UN special envoy called for a January 25 start date for talks among Syria's warring parties to end nearly five years of civil war.
A spokesman for Staffan de Mistura said the special envoy wants "the broadest possible spectrum of the Syrian opposition and others" at the talks in Geneva.
“Continuing developments on the ground should not be allowed to derail” the talks, the statement said.
The statement appeared timed to the death of a top Syrian rebel commander, Zahran Allush, who was killed in air strikes that targeted the group's headquarters on December 25.
A number of other senior commanders of his Army of Islam group were also killed.
The Army of Islam is one of the most powerful groups battling Syrian President Bashar al-Assad's forces
Syrian military forces claimed responsibility for the strikе, although many opposition groups blamed Russia, which has been bombing Islamic State targets and other insurgent groups since late September.
Allush’s assassination dealt a significant setback to the opposition and could reshuffle the lineup of key players on the ground ahead of the planned Geneva talks.
The assassination "makes a mockery of all talk of a political settlement" and undermines the "negotiations before they begin,” Anas al-Abdeh, a senior member of the main Western-backed opposition group, the Syrian National Coalition, told the AP.
The talks scheduled for Geneva were authorized by a UN Security Council resolution, unanimously approved on December 18, that endorsed a road map for a Syrian peace process. It was a rare show of unity among major powers.
More than 250,000 people have been killed in the war that grew out of a Syrian government crackdown on a pro-democracy movement in early 2011.
Islamic State militants have used the chaos to seize territory in Syria and Iraq, and some 4.3 million Syrians have fled.
"The people of Syria have suffered enough," the UN statement said.