Tibet's capital Lhasa was under tight security as it prepared to host the Olympic Games torch on Saturday in a show of China's grip over the region, with officials claiming independence activists planned sabotage.

Baima Chilin, a vice chairman of Tibet's government, said supporters of the Dalai Lama, the exiled Tibetan Buddhist leader, wanted to upset the passage of the torch through Lhasa, where protests and riots challenged Chinese control in March.

"The Tibet independence forces have indeed been engaged in activities to sabotage the Olympic torch relay in Lhasa," he said. But with Lhasa's streets heavy with troops and police, he said he did not expect such attempts to succeed.

"We have full confidence and full ability to successfully complete the torch relay tomorrow," he told a news conference.

Baima Chilin's claim and the strict security around Lhasa underscored political tensions that are likely to greet the Olympic torch run on Saturday, when it will start on a city square and end below the Potala Palace, the Dalai Lama's towering traditional seat of power, in Lhasa.

As a group of foreign journalists arrived in Lhasa to observe the relay, police stood on guard every 200 metres. Trucks full of troops and riot police were also present.

Slogans on billboards and village walls welcomed the Olympics and urged locals not to cause trouble for the torch relay that will pass through Lhasa at 3,650 metres (12,000 feet) above sea level on Saturday before strictly vetted crowds.

"Protect social order and stability," read one sign.

"Harmoniously greet the Olympic Games," read another.

Police searched passers-by near the Potala. One stallholder said families were told to stay at home during the torch procession.

STARK SECURITY

The ancient centre of Tibetan Buddhist civilisation will be on show over three months after anti-government protests and deadly anti-Chinese riots erupted in March, sparking protests in Tibetan areas that were quelled by a massive troop influx.

While authorities have spared no efforts to ensure fresh anti-China gestures do not upset the Olympic flame's procession this time, the stark security surrounding it will be a constant reminder of the tensions left after recent unrest.

The Lhasa relay has been drastically shortened from the 27 kilometres first planned to 9 kilometres, and will have 156 torch bearers, including 75 ethnic Tibetans, Dekyi Drolkar of the regional sports authority said.

She said the change was out of respect for victims of China's devastating quake, not a response to potential protest.

China blamed the "clique" of the Dalai Lama, the exiled Buddhist leader revered by most Tibetans, for instigating the unrest to upset the Olympics in August. The Dalai has denied that claim and said he supports the Games. But many exiled Tibetans oppose the Games, and especially the Tibet torch relay.

"Since this is a proud moment for the people of China, the Dalai Lama has appealed to Tibetans not to protest," Tenzin Taklha, a senior aide to the Dalai Lama, said from Dharamsala, the home of Tibet's government in exile.

Contrary to China's vows to allow unimpeded media access in the lead-up to the Games, only a selected group of journalists accompanied by officials was allowed to Lhasa for the relay, and the city remains off bounds to free reporting.

"Lhasa is a city of fear and intimidation whose residents live under constant surveillance," Phelim Kine of the New York-based advocacy group Human Rights Watch said in an email.

Authorities have told Lhasa residents that they "are ready and willing to 'severely punish' and 'give no indulgence'" to any attempted disruption of the torch run, Kine said.