U.S. Secretary of State John Kerry is still pursuing an agreement with Russia on military cooperation in the fight against the Islamic State group in Syria despite major setbacks and skepticism from other administration officials and U.S. allies, U.S. officials with knowledge of the talks said on Friday.

"We believe this approach is still worth pursuing," State Department spokesman John Kirby said in an emailed response to questions, adding: "But it remains to be seen whether or not we can get there."

Kerry has been pursuing a proposal that envisions resuscitating a Cessation of Hostilities agreement, creating a center where the two countries would share intelligence for targeting airstrikes, and prohibiting the Syrian air force from attacking U.S.-backed rebel groups.