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The Latest: US claims Tabqa dam is not in danger of bursting

BEIRUT (AP) — The Latest on the Syrian conflict (all times local):

10 p.m.

U.S.-led coalition forces say the Tabqa Dam in northern Syria is structurally sound.

The Islamic State group claimed Sunday that coalition airstrikes had locked the dam's gates, causing Euphrates River water levels to rise dangerously behind the structure. The group warned the dam could burst.

The coalition denied the report in a letter to The Associated Press, saying U.S.-backed Syrian Kurdish forces were in control of a spillway north of the dam "which can be used to alleviate pressure on the dam if need be."

The U.S. has provided substantial air and ground support to the Kurdish-led Syrian Democratic Forces, who are closing in on the IS capital Raqqa, 40 kilometers (25 miles) upstream from Tabqa Dam.

The coalition says the dam has not been structurally damaged, to its knowledge, and says it has not targeted the dam.

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9:45 p.m.

U.S.-backed Syrian Kurdish forces say they have captured the Tabqa air base in northern Syria from Islamic State militants.

The Kurdish-led Syrian Democratic Forces say they captured the strategically located air base from the militant group on Sunday, 45 kilometers (28 miles) west of Raqqa, the Islamic State group's de facto capital in Syria.

It is the first major acquisition for the group since U.S. forces airlifted hundreds of SDF forces, as well as U.S. military advisers and U.S. artillery, behind IS lines five days ago.

The U.S. has provided substantial air and ground support to the SDF, who are closing in on the IS capital.

Tabqa air base was captured by IS militants from the Syrian government in August 2014. Shortly afterward, the group announced it had killed about 200 government soldiers at the base, in a mass killing recorded and distributed on video over social media.

The Britain-based Syrian Observatory for Human Rights monitoring group also reported the SDF victory.

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7 p.m.

Syrian activists say U.S.-backed Syrian Kurdish forces have reached the Tabqa air base in northern Syria and are fighting to seize it from Islamic State control.

The Britain-based Syrian Observatory for Human Rights says the Kurdish-led Syrian Democratic Forces are firing on Islamic State militants inside the air base, which they seized from the Syrian government in 2014.

The activist-run Raqqa is Being Slaughtered Silently says the SDF have "controlled" several parts of the air base, while the media arm for the Kurdish PYD political party, which is aligned with the SDF, says fighters have seized a village one kilometer (0.6 miles) away from the air base.

The air base lies 45 kilometers (28 miles) west of Raqqa, the Islamic State group's de facto capital in Syria.

The U.S. has provided substantial air and ground support to the SDF, who are closing in on the IS capital.

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2:45 p.m.

Syrian activists say the Islamic State group has ordered an evacuation from its de facto capital, Raqqa, following warnings that the Tabqa Dam upstream on the Euphrates River could collapse.

The activist-run Raqqa is Being Slaughtered Silently says civilians are fleeing Raqqa en masse. It says the militants are warning residents that the dam is out of service, weakened by U.S.-led coalition airstrikes, and could collapse. It says water levels are rising behind the dam.

The Britain-based Syrian Observatory for Human Rights, an opposition-run monitoring group, is also reporting the dam is out of service.

The two groups rely on local contacts to smuggle information out of IS-held territory.

U.S.-backed Syrian Kurdish forces are battling IS near the militant-held dam as part of a broader campaign to take Raqqa.

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2 p.m.

A leading Syrian opposition group is calling on the U.S.-led coalition to stop targeting residential areas in and around Raqqa, the Islamic State group's de facto capital.

The Syrian National Coalition says it is "increasingly concerned" about civilian casualties in the campaign against the extremist group. The exiled opposition coalition is taking part in U.N.-mediated talks in Geneva.

The SNC says it believes coalition forces were behind an airstrike that killed at least 30 civilians sheltering in a school in the countryside outside Raqqa on March 21. The coalition has said it is investigating.

The U.S. has provided substantial air and ground support to the Kurdish-led Syrian Democratic Forces, who are closing in on Raqqa.