U.S. State Department spokesman Ian Kelly confirmed on Wednesday that U.S. special envoy to the Democratic People's Republic of Korea (DPRK) Stephen Bosworth had delivered President Barack Obama's letter to the country's top leader Kim Jong Il during his visit last week.

However, Bosworth said he brought no reply back.

"I can only confirm there was such a letter," Kelly said during a regular briefing in the State Department, refusing to discuss the content and tone of the message. He said sometimes diplomacy" is best conducted in a private and confidential way."

But he reassured that one can feel confident the letter concerned the "simple agenda" for the visit of Bosworth, which was to get the DPRK to come back to the six-party talks.

Bosworth conducted a three-day visit to the DPRK last week, becoming the highest-ranking U.S. official to visit the country since Obama took office.

Bosworth himself refused to confirm the existence of Obama's letter earlier in a State Department briefing, telling reporters, "I was the message."

He said he was conveying directly to the DPRK leadership "a vision for the future which would be a lot different than the present or the past."

No reply back

Bosworth said he didn't bring any letter back from Kim for Obama. Kelly also said he wasn't aware if there was a reply from Pyongyang.

The spokesman said the ambassador handed the letter over to the DPRK government, not Kim Jong Il himself. Bosworth said the U.S. side didn't request a meeting with Kim.

According to the administration, Bosworth's visit was to see if the DPRK is prepared to return to the six-party talks and to reaffirm its commitments under the 2005 joint communique. Last week, Secretary of State Hillary Rodham Clinton said the visit was "quite positive" for a preliminary meeting.

Bosworth held talks with the DPRK's First Vice Foreign Minister Kang Sok-ju and Vice Foreign Minister Kim Kye-gwan, and communicated Obama's view that "complete denuclearization of the Korean Peninsula is the fundamental undertaking of the six-party talks, if resumed."

The DPRK shut down Yongbyon nuclear facilities in 2007 under a six-nation nuclear disarmament deal. However, the talks were then deadlocked over UN sanctions for the DPRK's missile and nuclear tests. In April, Pyongyang quit the six-party talks and announced it was resuming the reprocessing of plutonium from spent fuel rods at the reactor there.

It conducted an underground nuclear test in May and declared it was in the final phase of an experimental, highly enriched uranium program -- another way to make an atomic bomb.

However, tensions began to thaw recently, and the DPRK has expressed willingness to return to the six-party talks involving itself, the United States, China, the Republic of Korea, Japan and Russia, if it had satisfactory talks with Washington.