WASHINGTON (AP) — A senior U.S. envoy will travel to North Korea this week to seek the release of an American sentenced to 15 years of hard labor in the authoritarian country, the State Department said Tuesday.

The visit by Bob King, the U.S. special envoy for North Korean human rights issues, will be the first public trip to North Korea by an administration official in more than two years and could provide an opening for an improvement in relations severely strained by Pyongyang's pursuit of nuclear weapons.

State Department spokeswoman Marie Harf said King will request a pardon and amnesty for 45-year-old Kenneth Bae on humanitarian grounds. Bae, a tour operator and Christian missionary, was arrested in November and accused of committing "hostile acts" against North Korea. He suffers multiple health problems and was recently hospitalized.

Washington has been calling for Pyongyang to grant amnesty since Bae was sentenced on April 30.

King will fly to Pyongyang on Friday from Tokyo on a U.S. military plane and fly out on Saturday.

"Ambassador King will request the DPRK pardon Mr. Bae and grant him special amnesty on humanitarian grounds so that he can be reunited with his family and seek medical treatment," the department said in a statement. DPRK refers to the Democratic People's Republic of Korea.

When King last visited North Korea in May 2011 to assess the impoverished North's food situation, he came home with Eddie Jun, the last American to be held then freed by Pyongyang. Jun, a Korean-American from California, was arrested for alleged unauthorized missionary work during several business trips to the country. He was released on humanitarian grounds.

Bae's sister in the Seattle area revealed earlier this month that he was moved from a labor camp to a hospital after losing more than 50 pounds. (23 kilograms). Terri Chung says her brother suffers from diabetes, an enlarged heart, liver problems and back pain.

According to U.S. officials, Washington first made its offer to send King to North Korea several weeks ago, but Pyongyang only recently took them up on the offer. Pyongyang has yet to declare it will release Bae.

North Korea and the U.S. do not have formal diplomatic relations, and their tenuous ties have been in a tailspin for more than a year after Pyongyang conducted long-range rocket launches and a February nuclear test in defiance of U.N. Security Council resolutions. When sanctions were then tightened, North Korea issued dire threats against the U.S. and its allies.

North Korea has dialed down its rhetoric in recent months and has moved to improve its relations with rival South Korea, a staunch U.S. ally. The two sides have agreed to reopen a shuttered, joint industrial park and hold reunions of Korean families divided since the 1950-53 Korean War.

North Korea, analysts say, has previously used detained Americans as bargaining chips in its standoff with the U.S. over its nuclear and missile programs. Multi-nation aid-for-disarmament talks have been on hold since 2009, and efforts by Washington to negotiate a freeze in the North's nuclear program in exchange for food aid collapsed 18 months ago.

Two senior Obama administration officials reportedly made secret visits to North Korea in 2012 in an effort to improve relations with the government of young leader Kim Jong Un, but apparently made little headway.

Bae is at least the sixth American detained in North Korea since 2009. The others were eventually allowed to leave without serving out their terms, some after prominent Americans, including former presidents Bill Clinton and Jimmy Carter, visited North Korea.

In an interview posted online by a pro-North Korean newspaper earlier this month, Bae requested that a high-ranking U.S. official should come to North Korea and seek a pardon for his release. It wasn't clear from the video whether Bae was speaking voluntarily.