BEIRUT — An Islamic State suicide bomber targeted a joint convoy of U.S. and allied Kurdish forces Monday in northern Syria, marking the second attack against U.S. troops in less than a week and further highlighting the dangers surrounding U.S. plans to withdraw forces after a declaration that the extremist group had been defeated.

The attack happened at a checkpoint on the edge of the town of Shaddadeh in the Hassakeh province, on a road used by local Kurdish fighters and the U.S.-led coalition fighting Islamic State militants near the Iraqi border.

U.S. military Col. Sean Ryan said there were no casualties among the U.S.-led coalition members.

Monday’s bombing came days after a suicide attack killed 19 people, including two U.S. service members and two American civilians, in the northern Syrian town of Manbij. That bombing, outside a popular restaurant frequented by American troops, was the deadliest assault on U.S. troops in Syria since American forces moved into the country in 2015.

The extremist group claimed responsibility for both attacks in statements carried by its Aamaq news agency. Islamic State has been driven from virtually all the territory it once held in Syria and Iraq but continues to carry out attacks in both countries.

The Kurdish Hawar news agency, based in northern Syria, posted a video showing smoke rising from a vehicle on a desert road. Another video released by the Britain-based Syrian Observatory for Human Rights showed smoke rising from what appeared to be an armored vehicle belonging to the Syrian Kurdish militia in flames. Coalition armored vehicles and ambulances could be seen on the road.

In a Dec. 19 tweet announcing the withdrawal from Syria, President Trump declared, “We have defeated ISIS in Syria, my only reason for being there during the Trump presidency.” He said the troops would begin coming home “now.” That plan triggered immediate pushback from military leaders and led to the resignation of Defense Secretary Jim Mattis.

Over the past month, Trump and others have appeared to adjust the timeline, and U.S. officials have suggested it will likely take several months to safely withdraw the roughly 2,000 U.S. troops from Syria.

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