Joseph Yun, who visited Pyongyang in the process of negotiations that culminated in the release of 22-year-old University of Virginia student Otto Warmbier, met with the "three Americans who are being held there," the State Department said Thursday.
It was not clear whether they were in good health.
"In terms of their medical condition, that's something I cannot comment on," said State Department spokeswoman Heather Nauert. "The other day I said I won't comment on personal health matters, and so I'm going to stand by that."
Warmbier is in stable condition since his repatriation to his home state of Ohio, but doctors say the former detainee is unresponsive and has severely damaged brain tissue.
In May, Yun met with senior North Korean officials during informal talks in Norway. The U.S. diplomat was eventually allowed to travel to Pyongyang to see the detainees, after learning of Warmbier's condition on June 6.
On Monday, Yun and two physicians medically evacuated Warmbier. North Korea has since claimed it allowed the repatriation on humanitarian grounds.
Calls are growing for the release of the other hostages, including Hyeon Soo Lim, a South Korea-born Canadian pastor who has been detained since January 2015.
An online petition has gathered about 185,000 signatures calling for Lim's release, Radio Free Asia reported.
North Korea continues to detain three Americans: Kim Dong Chul, a Virginia businessman; Kim Sang Duk, a university professor; and Kim Hak-dong, also a university professor.