A high-ranking U.S. official familiar with North Korean affairs says it is true the North's leader, Kim Jong-il, collapsed due to an illness, but that it can't be concluded if it was due to a stroke.

The official, who chose not to disclose his name, told Radio Free Asia that the leader seems to be healthy enough to make decisions regarding the reactivation of its Yongbyon nuclear plant, adding it is unimaginable that such decisions would be made without his consent.

The Washington-based media outlet quoted the official as saying he currently believes that Kim still controls the country's state affairs.