State Department officials said that the letter was delivered last week by the administration's special envoy on North Korea.
U.S. officials say President Barack Obama has sent a letter to North Korean leader Kim Jong Il as international efforts to get Pyongyang to return to talks on its nuclear program intensify.
Speaking on condition of anonymity, State Department officials said that the letter was delivered last week when the administration's special envoy on North Korea, Stephen Bosworth, traveled to Pyongyang.
Officials declined, however, to comment on its contents.
It is relatively unusual for an American president to send the North Korean leader a personal letter so early in his term.
Former Presidents George W. Bush and Bill Clinton also sent letters to Mr. Kim, but not as early in their terms and only after efforts to restrain the North's nuclear ambitions.
Following Bosworth's visit to North Korea last week, he said officials in Pyongyang did not agree to a timetable to resume six-party talks on ending its nuclear weapons program. They did, however, acknowledge the importance of the six-party process.
On Monday, Bosworth said Washington and its partners in the talks want to restart negotiations with Pyongyang as soon as possible.
Bosworth's three-day visit to Pyongyang was the first high-level direct contact between the two sides since U.S. President Barack Obama took office.
The other parties to the negotiations with Pyongyang include South Korea, China and Japan.
Some information for this report was provided by AP and AFP.