The report came as China ramps up security ahead of the summer Games, set to begin on Aug 8 in the capital Beijing and several other cities, including Shanghai.

'We have obtained information that international terrorist organisations would likely launch an attack against an Olympic venue in the city during the Games,' the official Xinhua news agency quoted the head of Shanghai's Olympic security office, Mr Cheng Jiulong, as saying.

'We have staged raids and cracked a group of terrorists.'

The report did not specify when the operation took place or how many suspects were detained. Police officials were not immediately available for comment.

Mr Cheng said the Olympic football venue in Shanghai and housing for the players were now 'at a safe level'. But he added that the threat of a terror attack still existed.

Earlier in the day, state media reported that Chinese paramilitary police swore to prevent terrorist attacks or 'political incidents' from disrupting the Beijing Olympics, in a show of force at the main stadium of the Games.

The People's Armed Police News reported: 'International terrorist forces are itching to strike with terror attacks against the Beijing Games, and hostile domestic forces' disruption and sabotage activities against the Games are steadily unfolding.'

Earlier this month, local reports said police arrested 82 suspected terrorists in Xinjiang involved in plotting attacks on the Olympics.

Chinese officials have warned of an unprecedented threat to the Olympics, particularly from China's restive Muslim Xinjiang region in the north-west. They said the security of athletes and tourists remained their top priority.

Critics, however, have accused China's communist rulers of exaggerating the security threat to suppress domestic dissent and to clamp down on any form of protest during the Olympics.

Shanghai police had been placed on a 'crisis' footing as part of efforts to ensure public safety in the the city, Xinhua said.

The financial hub will host 12 Olympic football matches during next month's summer Games. According to Xinhua, the stadium has been closed since last Sunday, with armed police conducting round-the-clock patrols.

Firefighters, engineers and medical staff would be deployed to the stadium to prevent bomb blasts and nuclear and biochemical attacks.

Random identity checks would also be conducted near the venue and in other well-travelled parts of the city in the lead-up to the Games, Xinhua quoted Mr Cheng as saying.

He said security personnel should 'spare no effort to maintain law and order in the city'.

An official with the Shanghai public security bureau, Mr Hu Shunkang, said surveillance cameras had been installed on 1,500 public buses that regularly passed the stadium, according to Xinhua.

Extra security checkpoints had also been set up at underground rail stations.

Shanghai had also moved to block foreign businessmen from visiting during the Olympics. Invitation letters provided by the authorities to support visa applications had been postponed until after the Games.

A report on china.org.cn, the Chinese government's Internet portal, said yesterday that 24-hour security would be provided at the hotels where athletes were staying.

The site also quoted officials as saying that members of the public who provided information on 'violent terror attacks, illegal domestic and foreign organisations...and serious public security and criminal incidents' would receive rewards ranging from 10,000 yuan to 500,000 yuan (S$1,993 to S$99,650).

AGENCE FRANCE-PRESSE, REUTERS