WASHINGTON—Kim Jong Nam, the slain half brother of North Korea’s leader, was a Central Intelligence Agency source who met on several occasions with agency operatives, a person knowledgeable about the matter said.

“There was a nexus” between the U.S. spy agency and Mr. Kim, the person said.

Mr. Kim, the half brother of North Korean leader Kim Jong Un, was killed in Kuala Lumpur International Airport in Malaysia in February 2017, when two women smeared his face with the nerve agent VX. U.S. and South Korean officials have blamed the attack on North Korea, which it denies.

Many details of Mr. Kim’s relationship with the CIA remain unclear. Several former U.S. officials said the half brother, who had lived outside of North Korea for many years and had no known power base in Pyongyang, was unlikely to be able to provide details of the secretive country’s inner workings.

They also said Mr. Kim—who resided mainly in the Chinese enclave of Macau—was almost certainly in contact with security services of other countries, particularly China’s. The CIA declined to comment. Chinese officials didn’t respond to a request for comment.