The unprecedented formalities behind North Korea's release of three Americans have drawn attention, as Pyongyang's media said Thursday that they were all set free by an amnesty granted by the chairman of the North's State Affairs Commission.

Reporting on North Korean leader Kim Jong-un's meeting with US Secretary of State Mike Pompeo in Pyongyang on Wednesday, the Korean Central News Agency said that Kim issued an order as chairman of the State Affairs Commission on granting amnesty to the Americans for their repatriation.

The three Korean Americans -- Kim Hak-song, Tony Kim and Kim Dong-chul -- were detained in North Korea on charges of espionage or "hostile acts" against the regime.

Pyongyang has detained and released US civilian prisoners on several occasions during Kim's reign, but this is the first time that Americans have been released via an amnesty from the North Korean leader.

The Kim Jong-un regime enforced a special pardon for North Korean residents on the centenary of the birth of state founder Kim Il-sung in 2012 and the 70th founding anniversary of the Workers' Party in 2015.

But it is unprecedented for the North to release foreigners in accordance with amnesty procedures.

An American national was expelled from North Korea in December 2013, while another US citizen was repatriated without condition in October 2014. At that time, the North's media said the American prisoner was released under a "special measure" by the North's leader.

In November 2014, two other Americans were repatriated but Pyongyang's media did not announce their release.

When repatriating unconscious US student Otto Warmbier in June last year, North Korea explained that he was sent home "on humanitarian grounds."

North Korea watchers speculate that the North's emphasis on its top leader's exercise of amnesty is seen as an effort to indicate the Kim regime adheres to law and protocol in its external policy.

They also say that Kim's issuance of an order to release the Americans in front of Pompeo is a goodwill gesture to show Trump that the North is serious about improving relations with the US.

"Chairman Kim Jong-un's amnesty order for detained Americans is a goodwill message towards the US as well as an attempt to emphasize the power of the North Korean leader," Jang Chul-un, a professor at Kyungnam University, said. (Yonhap)