North Korea has canceled for a second time its invitation for a senior U.S. envoy to visit the country to discuss a long-detained American's possible release, the State Department said Monday.

The cancellation comes only days after detained American missionary Kenneth Bae told a pro-Pyongyang newspaper that he expected to meet this month with the envoy. It signals an apparent protest of upcoming annual military drills between Washington and Seoul and an alleged mobilization of U.S. nuclear-capable B-52 bombers during training near the Korean Peninsula. North Korea calls the planned drills a rehearsal for invasion, a claim the allies deny.

The State Department also said in a statement that civil rights leader the Rev. Jesse Jackson has offered to travel to North Korea at the request of Bae's family. The State Department did not elaborate and referred questions to Jackson, whose spokesman didn't immediately respond to a request for comment.

Analysts say North Korea has previously used detained Americans as leverage in its standoff with the U.S. over its nuclear and missile programs; North Korea denies this.

Bae has been held in North Korea for 15 months. The North accused him of smuggling in inflammatory literature and trying to establish a base for anti-government activities at a border city hotel.

Bae was quoted last week in an interview with the Japan-based Choson Sinbo newspaper as saying that a Swedish diplomat told him the U.S. envoy on North Korean human rights issues, Bob King, would visit him as early as Monday and no later than the end of the month.

Bae said he also heard from the diplomat that the U.S. government had told North Korea that it intends to send the Rev. Jackson, but the North instead allowed King to come to the country, the report said, without elaborating.

The U.S. and North Korea, which fought the 1950-53 Korean War, have no diplomatic relations. The Swedish Embassy in Pyongyang handles consular matters there for the U.S.

"We are deeply disappointed by the DPRK decision – for a second time – to rescind its invitation for Ambassador King to travel to Pyongyang to discuss Kenneth Bae's release,'' State Department spokeswoman Jen Psaki said. DPRK stands for the Democratic People's Republic of Korea, the North's official name.

She said the upcoming military drills with South Korea are "in no way linked to Mr. Bae's case,'' and that Washington remains prepared to send King to North Korea in support of Bae's release.

In August, North Korea also rescinded an invitation for King to visit, saying Washington perpetrated a grave provocation by flying B-52 bombers during previous military drills with South Korea. Last week, North Korea threatened to scrap reunions of war-divided families in the two Koreas later this month because of the upcoming drills and the alleged B-52 flights.

The U.S. Pacific Command wouldn't confirm the North's bomber flight claim but said it has maintained a strategic bomber presence in the region for more than a decade. South Korea's Defense Ministry said Monday that two sets of South Korea-U.S. military drills will begin on Feb. 24 and the second, longer one will run until April 18.

U.S. Secretary of State John Kerry is to visit Seoul on Thursday and Friday for talks on North Korea as part of an Asian tour, according to the State Department and Seoul's Foreign Ministry.

"North Korea appears to be more scared about the B-52s than (about ordinary U.S. military drills) ... because the bombers can conduct precision strikes against the headquarters of the country's leadership,'' said analyst Cheong Seong-jang at the private Sejong Institute in South Korea.

North Korea has recently toned down its typical harsh rhetoric against South Korea and made a series of conciliatory gestures, and outside observers link this softening to its need for improved ties with the outside world in order to attract foreign investment and aid.

Cheong said talks on Bae's release will likely come only after the U.S.-South Korea drills end in April.

Bae's sister, Terri Chung of Edmonds, Washington, said Friday that her family learned from the U.S. State Department that Bae, 45, had been taken back to a labor camp from a hospital where he had been treated after losing 50 pounds (22.6 kilograms).

Bae, who led tour groups in North Korea, has been serving 15 years of hard labor. His family says he suffers from diabetes, an enlarged heart, liver problems and back pain. In the Choson Sinbo interview, Bae said he does eight hours of labor per day and suffers pain in his legs and back.

Meanwhile, Donald Gregg, a former U.S. ambassador to South Korea, arrived in Pyongyang on Monday with representatives of the Pacific Century Institute, a private U.S. group. Gregg, who is chairman of the institute, wouldn't say what he hoped to discuss there. Another group member and former U.S. diplomat, Lynn Turk, said they were invited by the North Korean Foreign Ministry and their aim is to discuss how to "build bridges'' between the countries. (AP)