"We will watch closely how this relationship develops," Scaparrotti told the Aspen Security Forum in Colorado on Thursday. "I would be concerned if they were departing from the values that are the bedrock of the Washington Treaty [founding NATO] — the rule of law."
Turkish President Recep Tayyip Erdogan is scheduled to meet Russian President Vladimir Putin next month.
"We encouraged Turkey to try and recover from the shootdown and solve that problem with the Russians so that was good," Scaparrotti added.
In June Erdogan apologized to Russia and Putin for the shooting down of a Russian Sukhoi bomber carrying out strikes against Islamist targets in Syria last year.