The American campaign to remove the Islamic State from northern Syria continues to be complicated by the various armed groups and allegiances on the ground.

Turkey, a critical ally for the United States in counter-terrorism operations in the region, has expressed great concern over American support for the Kurdish YPG, an armed group fighting against the Islamic State that Turkey considers a terrorist organization.

According to Turkey, the YPG is a close associate with the Kurdistan Workers Party (PKK), which has conducted a series of terrorist attacks and is waging an ongoing insurgency inside Turkey.

Turkish Prime Minister Binali Yildirim called the American support for the YPG ‘unfortunate’ in a news conference yesterday.