PYONGYANG, North Korea >> The United States government must make a formal apology to secure the freedom of two Americans who remain imprisoned in North Korea after the release this week of Jeffrey Fowle, North Korean legal experts said Thursday.

Although North Korea released Fowle, getting Matthew Miller and Kenneth Bae out of prison will likely require an official statement of apology and formal request for their release from Washington, according to the two North Korean law experts who spoke to The Associated Press.

Fowle, who had not yet been tried in a court, was flown out of North Korea on a U.S. military jet on Tuesday after being detained for six months for leaving a Bible in a nightclub in the city of Chongjin, where he was visiting with a foreign tour group. North Korean state media said he was released after leader Kim Jong Un granted him a special pardon following "repeated requests" from President Barack Obama.

There has been no word on whether any progress has been made toward getting Miller and Bae released as well.

"In order to return the prisoners to their country, the United States must make an official apology and request their release," said Sok Chol Won, a professor of international law at Pyongyang’s Academy of Social Sciences.

Fowle’s release came after the North Korean government made several appeals through its state-run media for Washington to take steps to resolve the matter. The three men were also allowed to meet several times with The Associated Press and other media to plea for help and keep the issue on Washington’s radar.

Miller and Bae were charged with more serious crimes than Fowle and have already been convicted by North Korea’s Supreme Court.

Miller, who entered the country on April 10 on a tourist visa, allegedly ripped up the document at Pyongyang’s airport and demanded asylum. North Korean authorities say he intended to conduct espionage while in the country. He was convicted and sentenced to six years in prison. During his brief trial six weeks ago, North Korean prosecutors said he admitted having the "wild ambition" of experiencing prison life so that he could secretly investigate North Korea’s human rights situation.

He is now digging in fields at a labor camp eight hours a day and being kept in isolation.

Bae, 46, has been held since November 2012, when he was detained while leading a tour group in a special North Korean economic zone. He was sentenced to 15 years in prison for "hostile acts" after being accused of smuggling in inflammatory literature and trying to establish a base for anti-government activities at a border city hotel. Bae is a Korean-American missionary, and his family believes he was detained because of his Christian faith.

Bae is suffering from chronic health issues.

"It’s not a matter of individuals. It’s between countries," said Ri Kyong Chol, another law professor at the academy. "Between the U.S. and our country there is no political channel. … If there were diplomatic relations between our two countries this kind of problem wouldn’t happen."

Both Miller and Bae have told the AP they believe their only chance of release is the intervention of a high-ranking government official or a senior U.S. statesman.

In the past, former Vice President Al Gore and former President Jimmy Carter have come to Pyongyang to bring detainees back home.