SEOUL (AFP) - - After a troubled worldwide trip the Beijing Olympic torch Monday began its journey through the capital of communist North Korea, where thousands were mobilised to show support for close ally China.

TV footage showed crowds dressed in their best clothes packing the streets of Pyongyang as the torch began its 20-kilometre (12 mile) relay route. It was the first time the Olympic flame had been carried in North Korea.

In some other cities, the relay has sparked rowdy protests against China's policies on Tibet and other issues, but North Korea clamps down sharply on any dissent and the Pyongyang leg was guaranteed to run smoothly.

Reclusive leader Kim Jong-Il was absent from the launch ceremony at the Tower of the Juche Idea -- named after the impoverished state's guiding ideology of juche or self-reliance.

De facto head of state Kim Yong-Nam handed the torch to the first runner, a hero of one of the nation's greatest sporting triumphs.

"I am very honoured to have been chosen for this at my advanced age," Japan's Kyodo news agency quoted Pak Du-Ik, 71, as saying on Sunday.

Pak was a key member of the country's football team which advanced to the 1966 World Cup quarter-finals.

The torch has been dogged by demonstrators since the Olympic flame was lit last month, with critics of China's military crackdown in Tibet and its human rights record severely disrupting the Paris and London legs of the relay.

Organisers in many other countries have been forced to surround the torch with unprecedented security to ensure a smooth passage.

North Korea had earlier promised to "astonish the world" with its handling of the relay and criticised the overseas protests.

Radio Pyongyang on Monday slammed the demonstrations as "an open challenge to the spirit and charter of the Olympics," according to Seoul's Yonhap news agency.

During the South Korean leg Sunday, demonstrators including North Korean defectors staged protests against China's forced repatriation of refugees from the North.

There were sporadic clashes in Seoul between protesters and thousands of Chinese students.

China sends back all those North Koreans it catches as economic migrants, a policy strongly criticised by rights groups. Refugees face severe punishment, or even a death sentence in some cases, on their return.

In Pyongyang, men in dark suits and women in traditional hanbok gowns waved artificial bunches of kimjongilia, a national flower named after the leader, as the relay got under way at 10:15 am.

Banners reading "Beijing 2008" were hung on both sides of the route.

A total of 80 people were due to carry the torch along the route, which ends at Kim Il-Sung Stadium at around 3:00 pm (0600 GMT).

Official media has said they include "officials of merit," famous athletes, working people, overseas Koreans and foreign residents.

Kyodo said almost three-quarters of the runners are North Koreans and the rest are Chinese nationals, including ambassador Liu Xiaoming.

The torch had arrived in North Korea early Monday by chartered plane direct from Seoul, to a welcome from nearly 1,000 locals and Chinese students.

The flame will be taken to Vietnam after North Korea and then to Hong Kong and Macau, before starting the final leg of the relay in mainland China.