The United States called Saturday for the "immediate release" of Merrill Newman, an elderly Californian detained in North Korea for alleged "hostile acts" against the reclusive, communist country.

The 85-year-old grandfather with heart problems was plucked off a plane last month as he was leaving Pyongyang following a tourist visit.

North Korea confirmed Saturday that an American veteran of the Korean War has been detained for "hostile acts" against the communist country and said he had released a written apology confessing to his alleged crimes.

Merrill Newman, an 85-year-old from California, was held in October after entering the North "under the guise of a tourist", the country's official KCNA news agency said.

North Korea has increased food production for a third straight year, but malnutrition remains widespread, U.N. agencies say, voicing particular concern over stunting in children.

Failures in the state distribution system mean families increasingly rely on unofficial markets and bartering to feed themselves, according to a nationwide assessment published Thursday by the Food and Agriculture Organization (FAO) and the World Food Program.

Activities observed at North Korea's Yongbyon site indicate an effort to restart a reactor that could provide it with weapons-grade plutonium, the U.N. atomic agency said Thursday.

"The Agency continues to monitor developments at the Yongbyon site, mainly through satellite imagery," International Atomic Energy Agency head Yukiya Amano said.

Panama will release 32 of 35 North Korean sailors detained for carrying undeclared Cuban arms as their ship was about to transit the Panama Canal, the Foreign Ministry said Wednesday.

Panamanian authorities seized the Chong Chon Gang on July 10 after discovering 25 shipping containers of Cuban military hardware, including two MiG-21 fighter jets, concealed in a sugar shipment.

North Korea on Wednesday slammed the United States for blocking denuclearization talks with "absurd preconditions" that would only prompt Pyongyang to bolster its nuclear deterrent capacity.

In a statement carried by the North's official Korean Central News Agency (KCNA), a Foreign Ministry spokesman said Pyongyang's search for a "negotiated settlement" on its nuclear program was being stymied by a "hostile" US policy.

North Korea has refused to accept an official written request from South Korea for the release of one of its citizens detained for alleged espionage, Seoul officials said Tuesday.

The unification ministry said it had been trying to deliver the request through the border truce village of Panmunjom since Monday.

Washington's point man on North Korea on Monday hinted at more sanctions against Pyongyang over its atomic weapons program in the wake of Iran's nuclear deal with world powers.

Glyn Davies, the U.S. special representative for North Korea policy, said he hoped quickening diplomacy examining when to resume stalled six-party talks would bear fruit.

North Korea on Friday marked the anniversary of its shelling of a South Korean border island with a threat to turn South Korea's presidential office into a "sea of fire.”

The threat came as the South's army, navy, air force and marine corps launched an intensive military drill on and around Yeonpyeong Island in memory of the incident in which four people were killed in November 2010.

U.S. Secretary of State John Kerry Thursday called for North Korea to release an 85-year-old pensioner and Korea War veteran who has been detained in the isolated country for more than three weeks.

Without mentioning Merrill Newman by name, Kerry told MSNBC television that his detention was one of many "disturbing choices by the North Koreans."