He also acknowledged some things still need to be worked out between Turkey and Kurdish forces, but remains confident of a positive outcome.
US President Donald Trump has threatened to "devastate Turkey economically" if it attacks Kurdish forces in Syria following a planned pullout of US troops.
Col. Ryan acknowledged the US withdrawal in Syria had commenced Friday, but withheld details of specific military plans on troop movements. "Will attack again from existing nearby base if it reforms", Trump said, using a different acronym for IS.
US Secretary of State Mike Pompeo earlier this month said that ensuring the Turkish military does not massacre the Kurds would be a key priority for the United States following the Pentagon's withdrawal of its troops from Syria.
Once the troops are gone, the USA will have ended three years of organizing, arming, advising and providing air cover for Syrian, Kurdish and Arab fighters in an open-ended campaign devised by the Obama administration to deal ISIS a lasting defeat.
"The withdrawal is based on operational conditions on the ground, including conversation with our allies and partners, and is not be subject to an arbitrary timeline", he said. But Turkish President Tayyip Erdogan has vowed to crush the Kurdish groups that have been effective in defeating IS in Syria.
Maria Zakharova, a Russian Foreign Ministry spokeswoman, said it was important for Syrian Kurds and the Syrian government to start talking to each other in light of the USA withdrawal plans.
Turkey had reacted angrily to previous suggestions that Trump's plan to withdraw troops was conditional on the safety of the US-backed Kurdish fighters, who are seen by the Turkish government as terrorists.
"We have no problems with our Kurdish brothers, Arab brothers in Syria, Turkmens and other ethnic and religious groups".
Washington, however, considers the group as an effective force in the fight against IS.
Turkey had rejected the US claim that the Syrian Kurds were represented by the YPG, which Ankara sees as a terrorist organization.
Israel has generally refrained from commenting about the strikes for fear of triggering a reaction and being drawn into the deadly fighting in neighboring Syria's civil war.
"We have achieved the goal that we set out to achieve", he said.
"We recognize the Turkish people's right and President Erdogan's to defend their country from terrorists", Pompeo said Saturday, according to NPR's Michele Kelemen, who is traveling with the secretary.