A US teenager who spent a week in North Korea to promote an idea for a peace forest on the tense Korean border said Thursday his trip had given him "hope" for the future of the peninsula.

Jonathan Lee, a 13-year-old ethnic Korean, said he felt safe and had been treated well during his visit to one of the most secretive states in the world.

Lee said that he headed to Pyongyang with a letter for North Korean leader Kim Jong-Il, proposing the creation of a "children's peace forest" in the demilitarised zone (DMZ) dividing North and South.

The trip comes amid high cross-border tensions, which grew after South Korea and the United States accused the North in May of torpedoing one of Seoul's warships with the loss of 46 lives.

"My letter suggesting this (idea) was passed on to Chairman Kim Jong-Il along with my book as a gift to him," Lee told reporters at Beijing airport, where he stopped for a layover with his parents before flying to Seoul.

"I went to several places but the place that made the biggest impression on me was the DMZ," said Lee, who hails from the southern US state of Mississippi.

"While at the DMZ, I spoke of my hope of having a children's peace forest. My suggestion for the motto is 'Above politics, above conflicts, above borders, above ideology'."

Lee has sent letters to South Korean President Lee Myung-Bak, US President Barack Obama and China's President Hu Jintao, explaining his idea for the peace forest of fruit and chestnut trees on the world's last Cold War frontier.

The surrounding area is heavily fortified with concrete, barbed wire, land mines and soldiers from both North and South Korea.

His visit recalled the efforts of 11-year-old US schoolgirl Samantha Smith, who in 1983 travelled to the Soviet Union at the height of the Cold War, after writing to then leader Yuri Andropov to ask if he planned a nuclear war against the US.

"It's all about giving hope to the people and children around the world," said Lee, the founder of a global youth environmental group called I.C.E.Y. H.O.P.E.

"On this trip, I discovered that both sides want reunification, and that Korea is one, so I see hope on the Korean peninsula."

He told South Korea's Yonhap news agency that North Korean officials had given a "good" response to his proposal, and that the country's people were "quite lively".

The teen also said officials had told his family that progress could be made on his idea only if the United States were to help transform the armistice that ended the 1950-53 Korean War into a full-fledged peace treaty.

North Korea, which has no diplomatic relations with the United States, approved Lee's trip despite a tense stand-off between the countries over the detention of four American citizens for illegal entry.

Three have been released but but Aijalon Gomes, a 30-year-old former English teacher in Seoul, is still being held in prison there.

Gomes was arrested in January and sentenced to eight years' hard labour for an illegal border crossing. The North said in July that Gomes had tried to commit suicide and was being treated in hospital.

Lee has previously said his idea was inspired by former South Korean leader Kim Dae-Jung, who died in August last year.

As president from 1998-2003, Kim Dae-Jung held a landmark summit with North Korea's Kim in 2000 that paved the way for inter-Korean reconciliation and earned him a Nobel peace prize.

related report
China special envoy visits North Korea
China said Thursday that a top envoy had visited North Korea this week for talks on the resumption of negotiations aimed at ending Pyongyang's nuclear drive, with tensions running high in the region.

The trip by the official, Wu Dawei, came as an aircraft believed to be a North Korean fighter jet crashed in China's northeast, killing the pilot, amid reports he might have been trying to escape the impoverished state.

Wu, China's special envoy on Korean affairs, travelled to North Korea on Monday and returned on Wednesday, the foreign ministry said in a statement.

Wu met North Korea's foreign minister and the head of the international department of the Korean Workers' Party Central Committee, it added.

He "exchanged views with North Korea about maintaining peace and stability on the Korean peninsula and restarting the process of the six-party talks," the ministry said.

The six-party nuclear disarmament talks -- which include the two Koreas, China, Japan, Russia and the United States -- have been stalled since Pyongyang stormed out in April last year.

Wu's visit comes amid high tensions in the region after the United States and South Korea conducted major joint naval exercises in the Sea of Japan (East Sea).

The military drills were aimed at warning North Korea -- China's ally -- after the sinking of a South Korean warship that Seoul and its allies say was carried out by a North Korean submarine.

Last week, Seoul also staged its largest-ever anti-submarine drill near the disputed Yellow Sea border.

Tensions escalated further after North Korea seized a South Korean squid fishing boat and fired artillery into the Yellow Sea when South Korea was wrapping up the anti-submarine exercise.