Also Monday, activists said rebels and pro-government Kurdish gunmen struck a truce to end days of fighting in the northern town of Ras al-Ayn near the border with Turkey that opposition forces entered earlier this month.
The Britain-based Syrian Observatory for Human Rights said rebel fighters overran regime defenses and captured the Tishrin Dam, near the town of Manbij, before dawn on Monday. Observatory direction Rami Abdul-Rahman said the dam supplies several areas of Syria with electricity.
"This is a major blow to the regime," said Abdul-Rahman by telephone describing the dam as "strategic location" on the Euphrates, which flows from Turkey in the north through Syria and into Iraq.
The rebels have scored a series of hard-fought strategic advances recently. On Sunday, they captured a regime helicopter base outside Damascus before pulling back for fear of government airstrikes.
Syria's conflict started in March 2011 as an uprising against President Bashar Assad's regime, inspired by other Arab Spring revolts. It quickly morphed into a civil war that has since killed more than 40,000 people, according to activists.
Amateur videos posted online showed gunmen inside the dam's operations room as an employee sat in front of five screens speaking by telephone about the level of water behind the dam. Another video showed gunman in front of dozens of green wooden boxes apparently full of munitions.
A gunman opened one of the boxes showing that it contained hand grenades. "The Free Syrian Army has fully liberated the Tishrin Dam," one of the rebels could be heard saying.
The activist videos appeared genuine and corresponded to other AP reporting about the events depicted. Syria restricts the access of reporters.
Also Monday, Kurdish activist Mustafa Osso and the Observatory's Abdul-Rahman said the town of Ras al-Ayn has been quiet since Saturday after fighters from the government-leaning Kurdish Democratic Union Party, or PYD, reached an agreement on a truce with rebels, most of them from Islamist extremist groups, including the al-Qaida-inspired Jabhat al-Nusra.
The rebels entered the town earlier this month and have since clashed almost daily with PYD gunmen for control over the area. Both factions add to the complexity of Syria's conflict, which has taken on heavy sectarian -- and ethnic -- overtones.
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The fighting in recent days has left dozens of people killed or wounded, and dozens captured on both sides. Osso and Abdul-Rahman said PYD forces and the rebels agreed to exchange prisoners and to withdraw their militiamen from the town.
Abdul-Rahman said the rival parties agreed to form a local council that will run day to day life in Ras al-Ayn. Osso said thousands of people who fled the town, which has a mixed population including Arabs, Kurds, Chechens and Christians, have started returning home.
A journalist in Ras al-Ayn told The Associated Press that the town has been calm since Saturday, adding that cars with PYD gunmen were seen in the streets with load speakers urging residents to return to their homes after the truce was reached. He added by telephone that parts of the town were heavily damaged by government air raids earlier this month.
When regime forces withdrew from Kurdish areas in northeastern Syria in July, they were quickly replaced by Kurdish fighters from PYD. Those forces then battled rebel fighters after they pushed their way into predominantly Kurdish areas. The Kurdish group is affiliated with the PKK, rebels fighting for autonomy in the Kurdish-dominated southeast region of Turkey.
The rebels, who Islamic militants, who are fighting on the side of the rebels, have played a bigger role in the Syrian conflict in recent months and many openly say they want to set up an Islamic state. The opposition is split, with some groups strongly opposed to the influence of extremists.
Press; By BASSEM MROUE]
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