An emotional Dennis Rodman appeared to break down Monday as he apologised on his return from a controversial trip to North Korea, where he sang "Happy Birthday" to regime leader Kim Jong-Un.

The former NBA star was widely criticised for refusing to bring up human rights abuses or the plight of a US missionary detained in North Korea during his week-long visit, but said he would return again next month.

Rodman was also accused of pandering to North Korean authorities during the trip, which featured an exhibition basketball match involving other NBA stars to mark Kim's birthday.

"I love my country, America, I love it and I will never trade it for nothing in the world," the pierced and heavily tattooed ex-Chicago Bull told reporters at Beijing airport.

Former world heavyweight boxing champion Mike Tyson has described Rodman's actions as "treason".

Rodman said he wanted to "show people that no matter what is going on in the world, for one day... not politics, not all this stuff..." before launching into an apology.

"I am sorry. I am not the president. I am not an ambassador. I am Dennis Rodman. Just an individual, just showing the world the fact that we can actually get along and be happy for one day," Rodman said, before his voice broke and he put his hands to his face.

The player known as "The Worm" was returning from his fourth visit to the reclusive state in 12 months.

"It is amazing that I had the opportunity just to go to North Korea, and for the Marshal (Kim) just to give me an opportunity just to be in his presence and in his city," he said, adding that he would visit the North again next month for "another game". He gave no further details.

Rodman has developed an unlikely relationship with the young North Korean leader since making his first trip there last February, when he declared Kim a "friend for life".

He enlisted an eclectic group of ex-NBA players for the exhibition match last Wednesday, before which he serenaded Kim -- in scenes compared to Marilyn Monroe singing to JFK -- and appeared to bow.

Former New York Knicks power forward Charles Smith told CNN Sunday that the players had been asked to return to the nuclear-armed state.

Another of Rodman's teammates, Eric 'Sleepy' Floyd, told ESPN that he was "misled" about the trip and he tried to leave the day after the players arrived last Monday as he was "uncomfortable" with not being given "all the information" about the itinerary.

Floyd said he believed he would be working with "kids" rather than attending a "birthday celebration" for Kim.

Rodman was Monday ushered through a heavy media presence by security and his entourage, which includes Joseph Terwilliger, a bearded tuba-playing neuroscience professor from Columbia University in New York.

The former power forward, who was wearing dark glasses, a blue tracksuit top and orange scarf, was asked whether he raised the issue of Kenneth Bae, who was detained by North Korean authorities.

In an interview with CNN last week, Rodman delivered an angry tirade in which he appeared to suggest that the missionary merited his 15-year prison sentence.

"I'm sorry I couldn't do anything," Rodman said, in comments echoing those of his publicist last week.

"I'm sorry, it's not my fault. I'm sorry... I just want to do some good stuff, that's all I want to do, basketball, that's all," he added.

Kim, who was educated in Switzerland, is reported to be a huge fan of basketball and especially of the Chicago Bulls, with whom Rodman won three NBA titles alongside Michael Jordan in the 1990s.

Bae was arrested in November 2012 as he entered Rason, a port in the northeast of the hardline Communist state.

North Korea, which bans religious proselytising, says that Bae was a Christian evangelist who brought in "inflammatory" material.