Students for a Free Tibet said five people - three Americans, a Briton and a Canadian - were detained by police after hanging the banner from the new headquarters of state-owned China Central Television, which is still under construction and is notable for having a shape likened to a twisted 'Z'.

Television footage of the protest by Britain's Sky News showed the activists draped in Tibetan nationalist flags and wearing helmets dangling from ropes as they hung the black-and-white banner about 20 feet (6 metres) off the ground.

Police quickly took the banner down.

Mr Wang Wenjie from the Beijing Public Security Bureau said he did not have any information on the protest and said he needed written questions before he could comment.

It was the latest in a series of protests by pro-Tibet and other activists who have sought to use the Olympic Games to criticize China for alleged repressive rule in Tibet, rights abuses and religious restrictions. Other foreign demonstrators have been quickly deported.

It also came a day after the International Olympic Committee urged China to allow foreign reporters at the games to report freely after a British journalist trying to cover a protest was allegedly roughed up by police.

Activists have also complained that protest zones designated by Beijing organisers were set up as a way to catch dissidents - not let them speak out. At least one person who applied to hold a demonstration in one of protest parks was detained by police.

An IOC spokeswoman was peppered on Thursday at a daily briefing with questions about an incident the day before in which a British TV journalist said he was manhandled and dragged into a police van while trying to cover an unauthorised protest by Tibet activists.

Police have said they mistook him for a protester.

Spokeswoman Giselle Davies said the committee disapproves of 'any attempts to hinder a journalist who is going about doing his job seemingly within the rules'.

'This, we hope, has been addressed. We don't want to see this happening again', she said.

In its bid to win the Olympics, China promised to loosen some aspects of its autocratic rule, including allowing the media to report freely and unblocking restricted websites for journalists.

It set up three protest parks, all well away from Olympic venues, in a gesture toward greater free speech.

But it said would-be protesters would have to apply for permission in advance. A week into the Beijing games, there has been no sign of demonstrations at the parks.

Sporadic flare-ups in other parts of the city suggest the absence of demonstrations is not for lack of dissent.

'It's clear to us that the protest zones are just a cynical public relations ploy on the part of the Chinese authorities', said Mr Lhadon Tethong of the New York-based Students for a Free Tibet.

'Sadly, I think the protest zones are just a trap at some level'. Beijing organising committee vice president Wang Wei on Thursday suggested critics were nitpicking.

He called the protest parks 'one step further for China to open up and I think it's (a) very good gesture'. -- AP