The U.S. should acknowledge Syria's PYD/YPG group is part of the PKK, Washington's former envoy to Ankara said on Friday."The PYD has at least expressed its difference with the PKK -- we cannot be deluded by that," Ambassador Francis Ricciardone said during remarks at the Association of Turkish American Associations' annual Washington gathering."Americans have to understand the PYD is part of the PKK. There's no sense in pretending otherwise," he added.Ties between Washington and Ankara have been strained over the PYD/YPG group with the U.S. insisting that it is an effective partner in the fight against Daesh.Turkish officials, however, say that it is the Syrian affiliate of the PKK, which has led a bloody campaign in Turkey for decades.Turkey, the U.S. and EU have designated the PKK group as a terrorist organization.The PYD/YPG has claimed it is "not the enemy of Turkey," Ricciardone said, urging the group "to act that way"."And it seems to me, the United States, if we're going to work with the PYD or any group that's associated with an enemy of Turkey-it has to prove its bonafides," he said."We cannot just pretend otherwise."The PKK renewed its armed campaign against Turkey in late July 2015.Since then, more than 280 members of Turkey's security forces have been killed and thousands of PKK terrorists killed in operations across Turkey and northern Iraq.