Tan Sri Abdul Aziz Zain, one of the four judges of the Royal Commission of Enquiry on the race riots, said that the commission could not find any evidence to support SM Lee's allegations.

Historian Professor Nik Anuar Nik Mahmud quoted American records to argue that the Americans too did not believe that Umno were involved.

They were responding to the statements in The Singapore Story: Memoirs of Lee Kuan Yew, launched last Wednesday, which suggested that Umno leaders were behind the race riots, which killed 23 people.

Yesterday, an article in The Sunday, a Malaysian tabloid, carried interviews with Tan Sri Aziz and Prof Nik Anuar, challenging SM Lee's version of the race riots.

Tan Sri Aziz, 76, a former federal court judge, recalled the evidence given to the commission.

A parade of Malays was passing along Geylang, he said, when a Chinese standing at a nearby first floor shop window, threw an empty bottle outside.

"It hit one of the participants of the parade. He fell down and bled profusely. When he was asked what happened, he answered that he was hit by a Chinese," he said.

Word then spread that the Chinese had disrupted the parade, upsetting the participants so much that they started hitting Chinese spectators along the road.

This small incident, according to the former judge, then escalated into a full scale riot.

But, although more than 10 people gave evidence to the commission, it is not clear what its conclusions were -- it was disbanded after only a month's work because of Singapore's split from Malaysia in Aug 1965.

On his part, Prof Nik Anuar, from the Universiti Kebangsaan Malaysia, told the newspaper that he was writing a book -- Singapore Within Malaysia: A Thorn in the Side -- and had formed his opinions after reading American and British records.

He argued that speeches made by Mr Lee in 1960s had stirred anti-Malay feelings among the non-Malays, while his attacks on Malay privileges had angered the Malays.

He cited an exchange between Malaysian Chinese Association MP Tan Toh Hong and an American diplomat in 1964, in which Mr Tan was recorded to have said: "The People's Action Party had done nothing for Singapore Malays but Lee had succeeded in tricking them into voting for him in the September elections by promising to improve their lot.

"When nothing was done in the following months, the Malays became disillusioned with Lee and when the eviction notices arrived they really became angry."

The notices were for villagers to move from their homes to make way for housing projects.

Prof Nik Anuar also cited a Sept 11, 1964 American embassy report which stated: "Umno took up the challenge and seized upon Malay discontent in Singapore, which had been growing without Umno's prior intervention, as a way of retaliating politically against Lee in his own political backyard."

Another US State Department report on July 27 1964, had quoted Mr Lee as saying that "Razak did not conspire with extremists", the historian noted.

Tun Abdul Razak was the Deputy Prime Minister at the time.

Prof Nik Anuar argued that while the Americans believed that Umno leaders may have taken advantage of the Singapore Malays' discontent to persuade them that they had misplaced their loyalties, they were not involved in the riots.