US President Donald Trump has welcomed home three American detainees released by North Korea.

Mr Trump said it was a "special night for these really great people" as they arrived at the Andrews Air Force Base near Washington.

The White House said the trio had been freed as a gesture of goodwill ahead of the planned meeting between Mr Trump and North Korean leader Kim Jong-un.

Mr Trump said he thought the summit would be "a big success".

• North Korea crisis in 300 words
• The tricky task of preparing for the summit

The date and location have been decided but not yet announced.

What did Mr Trump say when the men arrived home?

Mr Trump and his wife Melania entered the plane after it landed at about 02:45 local time (06:45 GMT) and a few minutes later emerged with the three men to wave to the media.

The president said he appreciated that Mr Kim had allowed the men to leave as "frankly we didn't think that was going to happen before the meeting".

Asked if this was his proudest achievement, he said that would be "when we denuclearise that entire peninsula".

"It's a great honour. But the true honour is going to be if we have a victory in getting rid of nuclear weapons."

Of the upcoming summit, he said: "I think that we're going to have... a very big success... I really think we have a very good chance of doing something very meaningful."

Mr Trump said he hoped he could travel to North Korea one day and that he believed Mr Kim wanted to bring his country "into the real world".

What have the freed detainees said?

The three men, Kim Hak-song, Tony Kim and Kim Dong-chul, were smiling and waving and appeared in good health.

In an impromptu chat before the media with Mr Trump, Kim Dong-chul said: "It's like a dream and we are very, very happy. We were treated in many different ways. For me, I had to do a lot of labour. But when I got sick I was also treated by them."

The three had released an earlier statement saying: "We would like to express our deep appreciation to the United States government, President Trump, Secretary [of State Mike] Pompeo and the people of the United States for bringing us home.

"We thank God and all our families and friends who prayed for us and for our return."

The trio had been jailed for anti-state activities and placed in labour camps.

How did the release come about?

It came during a visit to Pyongyang by Mr Pompeo to arrange details of the meeting between Mr Trump and Kim Jong-un.

Mr Kim said he had accepted a US proposal to grant the three detainees an amnesty, adding that his meeting with President Trump would be an "excellent first step" towards improving the situation on the Korean peninsula, according to the North Korean state news agency KCNA.

The convictions of the trio were widely condemned as political and an abuse of human rights.

Who are the freed Americans?

 Left to right: Kim Hak-song, Kim Dong-chul, Tony Kim

• Kim Hak-song was held on suspicion of "hostile acts" in May 2017. He had previously described himself as a Christian missionary who intended to start an experimental farm at the Pyongyang University of Science and Technology (PUST)
• Tony Kim, also known as Kim Sang-duk, also worked at PUST. He was detained in April 2017 on espionage charges. According to South Korean media, he had been involved in humanitarian work in the North
• Kim Dong-chul, a pastor in his early 60s, was detained in 2015 on spying charges, and was then sentenced to 10 years hard labour

Who are North Korea's American detainees?

What are North Korean prisons like?

Some 120,000 people are believed to be imprisoned in North Korea without due process, according to the Committee for Human Rights in North Korea (HRNK).

People can be jailed by the regime for almost anything, activists say, with crimes ranging from watching a South Korean DVD to trying to defect from the country.

Political prisoners are often sent to separate prisons - usually brutal labour camps, which involve difficult physical work such as mining and logging.

• How harsh is prison in North Korea?

Warmbier died less than a year after his tearful confession in Pyongyang

American missionary Kenneth Bae, who was sentenced to hard labour, later said he was forced to work on a farm six days a week despite being in poor health.

The last American to be freed - Otto Warmbier, who was jailed for stealing a hotel sign - was released last year but was fatally ill, and died shortly after returning home.

His parents, Fred and Cindy Warmbier, said they were "happy for the hostages and their families. We miss Otto".

Speaking at Andrews Air Force Base, Mr Trump said he wanted to pay his "warmest respects" to the couple.

How are the summit preparations going?

Mr Trump says the time, date and location will be announced "within three days".

He said the talks would not be held at the Demilitarized Zone (DMZ) that separates North and South Korea, one of the suggested venues, and Singapore remains the most likely option.

Mr Pompeo said there had been "good and productive conversations" with Mr Kim.

"We're planning it will be a single day, but in the event that there is more to discuss, there'll be an opportunity for it to extend into the second day as well," Mr Pompeo said.

The main issue, of course, will be North Korea's nuclear weapons, which Mr Trump has demanded Pyongyang give up.

There has been no word from North Korea on its agenda or what it might offer, although a key issue is certain to be the presence of 30,000 US military personnel in South Korea, along with the removal of sanctions.

At a summit in April, Kim Jong-un and South Korean President Moon Jae-in vowed to work to rid the peninsula of nuclear weapons, although the means of achieving this were not detailed and previous such pledges have been abandoned.