The US official, speaking on condition of anonymity, told the French agency two days after a summit between US President Donald Trump and North Korean leader Kim Jong-un in Hanoi did not result in any agreement. Both sides, however, are willing to keep the door open for dialogue.
The US NBC News website had earlier quoted US defense officials as saying that the Foal Eagle military exercises, usually held in the spring, had been postponed.
According to the agency, the joint military exercises organized by the two allies regularly raise the anger of Pyongyang, which sees it as a threat.
Previously, 200,000 South Korean troops and about 30,000 US troops were participating in joint military exercises.
But since the first Trump-Kim summit in Singapore in June, the United States and South Korea have reduced or canceled several joint military exercises, and US bombers are no longer flying over South Korea.
The US president has repeatedly complained about the cost of the exercises.
NBC pointed out that the annual exercise would be replaced by "limited and more task-related" maneuvers.