Washington (CNN) A "beautiful" letter from North Korean leader Kim Jong Un touted by President Donald Trump on Tuesday lacked substance and did not contain any details on a way forward for the stalled denuclearization talks between the two countries, according to a source familiar with its contents.

On the eve of the one-year anniversary of Trump and Kim Jong Un's first meeting in Singapore , Trump told reporters, "I just received a beautiful letter from Kim Jong Un ... I appreciated the letter."

Trump said he received the letter from Kim on Monday, the first since the February summit in Hanoi, which both leaders left empty-handed.

An administration official described the letter as a "birthday greeting." Trump's birthday is Friday and the official says Kim wished the President good health.

After months of stalled diplomacy Trump declared that North Korea was "not ready to negotiate" last month, but Monday's letter appeared to prompt him to take a more optimistic stance on the possibility of future talks.

"We have a very good relationship together," Trump said of Kim as he stood outside the White House on Tuesday. "Now I can confirm it because of the letter I got yesterday, and I think something will happen that's going to be very positive. But in the meantime, we have our hostages back, the remains keep coming back, we have a relationship."

Trump officials view the letter as a "reset" and setting the tone for a possible third summit. The administration official says the US is prepared for a third summit but is waiting to hear more from the North Koreans.

On Wednesday Trump called the letter "very nice" and "unexpected" but wouldn't elaborate on what was in it.

"Maybe in 100 years from now you'll see what was in that letter," he told reporters in a Rose Garden news conference with Polish President Andrzej Duda.

Trump's reaction was not out of the ordinary and the President has previously described notes from the North Korean dictator as "love letters." But in the past they have served as vehicles to plan -- or cancel -- summits between the two leaders.

Timing is crucial

The timing of the letter is key, explained two sources, who said that Kim planned the delivery before the anniversary of the leaders' first meeting to allow Trump to tout continued success. The letter did not issue any threats about cutting off communication completely or testing nuclear weapons, despite Kim having said earlier this year that he will wait until the end of this year for the United States to decide to be more flexible, according to North Korean media reports.

The State Department declined to comment on the content of the letter and the White House did not respond to a request for comment.

Despite stalled negotiations, US officials believe that Deputy Foreign Minister Choe Son Hui will be the new counterpart of US Special Representative to North Korea, Steve Biegun, but that has not been confirmed by the North Koreans. Biegun's previous counterpart, Kim Hyok Chol, is alive but he is being investigated for his role in the failed Hanoi summit.

On Monday, State Department Spokesperson Morgan Ortagus said that Biegun continues to work "diligently" on US-North Korea relations and noted that successful negotiations are "never linear."

As the Trump administration looks for ways to continue engagement with North Korea, Trump has repeatedly downplayed North Korea's latest test of a short-range ballistic missile. Yet his National Security Adviser John Bolton and acting Secretary of Defense Patrick Shanahan have both said that the tests violated UN resolutions.

Earlier Tuesday, Bolton had told the Wall Street Journal at an event in Washington that North Korea is not complying with the terms agreed upon during Trump's first summit with Kim, in Singapore last year.

"What they've said was that they're not going to test ballistic missiles, intercontinental range ballistic missiles, or have nuclear tests. That's continued. They're doing a lot of other things that still indicate that they have not made a strategic decision to give up the pursuit of deliverable weapons, which is why we continue the maximum pressure campaign," Bolton said.

CIA comments unhelpful but not an impediment

Trump also said on Tuesday that he would not have allowed the CIA to recruit Kim Jong Un's half-brother Kim Jong Nam, "under my auspices."

The comments were not helpful but were not seen as an impediment to US intelligence efforts, both sources said.

The administration official said using a relative as a spy is "asking for trouble" because history has shown relatives are unreliable, and that Trump was likely referring to that specifically.

Kim Jong Nam was a CIA asset. Trump and US officials would not confirm or deny the reporting from the Wall Street Journal thatwas a CIA asset.

Trump offered an equivocal response Wednesday when questioned about his Tuesday comments.

"It's not what I meant. It's what I said," Trump said when asked whether he meant the US should not use informants to spy on North Korea. "I think we are going to do very well with North Korea over a period of time."

Kim Jong Nam, once expected to be the heir to his father Kim Jong Il, had called himself a free spirit and traveled to many countries including France and Switzerland, explained an intelligence source. There is some speculation he met with intelligence officials in those countries as well. He was killed in February 2017 after two women smeared nerve agent on his face in Kuala Lumpur International Airport.