South Korean police said on Tuesday they arrested a man who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment.

The stone and wood structure Namdaemun, or "Great South Gate," was reduced to a charred hulk on Monday, with onlookers and newspaper editorials lamenting the loss of an iconic symbol of national pride.

The 69-year-old suspect was identified only by his family name Chae, said Namdaemun police station chief Kim Young-soo. Chae was taken into custody late on Monday and told police he had planned the arson for several months.

"The arsonist said he committed the crime out of anger because he felt the government did not take enough care with the appeal he filed after being insufficiently compensated for redevelopment in his residential area," Kim told a news conference.

Newspaper editorials on Tuesday said the loss of Namdaemun was an embarrassment that could have easily been prevented through better security and fire fighting measures.

The gate had withstood invasions, colonial occupation and was one of the few historic structures in Seoul to remain standing after the 1950-1953 Korean War.

"It was ruined in six hours due to our lack of care and attention," the mainstream JoongAng Ilbo newspaper said.

The conservative Dong-A Ilbo said: "The burden of guilt weighs heavily on our shoulders as we let one of Korea's most precious cultural properties turn into a heap of ashes."

Experts said a combination of structural design and misjudgement by nearly everyone involved led to the devastation.

"Without doubt the fire could have been controlled in the early stage," said Professor Lee Su-kyung of Seoul National University of Technology, had firefighters targeted the right spot.

Firefighters, who said they wanted to proceed cautiously to preserve Namdaemun, doused the structure with water but waited until it was too late to break through the roof to extinguish the fire inside, police officials said. By they time they acted, the blaze was out of control.

The gate was constructed in 1398 and served as the main southern entrance for Seoul when it became Korea's capital more than 600 years ago and was a walled city, the Cultural Heritage Administration said.

Namdaemun has also been the centrepiece of the country's international tourism campaign, with scores of tour buses making a stop each day before visitors are ushered to the nearby open-air market that shares the gate's name.

The structure, also called Sungnyemun or "Gate of Exalted Ceremonies", has been restored several times. The last major renovation took place in the early 1960s.

An official with the Cultural Heritage Administration said it would spend three years and 20 billion won (10.9 million pounds) to rebuild the structure.