At least 18 Kurdish YPG fighters and media officials were killed in Turkish air strikes on a headquarters of the militia in northeastern Syria on Tuesday, the British-based Syrian Observatory for Human Rights monitoring group said. The YPG, a U.S. ally in the fight against Islamic State, did not immediately give its own precise death toll. Turkey's military bombed the YPG and Kurdish militants in neighboring Iraq early on Tuesday, widening a campaign against groups affiliated with the outlawed Kurdistan Workers Party (PKK).