Oscar Pistorius began his T44 100 metres title defence with a smooth heat win on Wednesday but his complaints about rivals allegedly using longer blades will not be investigated further unless evidence is provided, the International Paralympic Committee (IPC) said.

Moments after a shock loss to Brazil's Alan Oliveira on Sunday, his first 200m defeat in nine years, South African Pistorius used a post-race interview to question the legitimacy of his defeat. Pistorius suggested that his opponent's prosthetics were too long which had artificially lengthened his stride, giving him an unfair advantage.

His comments sparked controversy and the South African, known as the "Blade Runner", later expressed regret over the timing of his outburst but the sprinter stuck to his complaint that IPC rules allowed athletes to have an artificially long stride length.

IPC communications director Craig Spence said the body had received a formal letter from the CEO of the South African Paralympic Committee requesting an urgent investigation into claims that athletes were using different size blades for semi-finals and finals and in different events.

Spence said they had found no evidence and it was "difficult for us to investigate any further".

"We met with coaches of the relevant athletes in the Village yesterday - I have to say there was quite a look of shock on the coaches' faces when we put this to them," Spence said on Wednesday.

"We will look at the measurements from the call room today, but we won't continue investigating unless the South Africans come to us with evidence."

Pistorius eased into Thursday's final by winning his 100 heat in 11.18 seconds.

World-record holder Jonnie Peacock of Britain set the fastest time with a heat one victory in 11.08, ahead of American Jerome Singleton and 200 gold medallist Oliveira, whose time was good enough for a final place.

Singleton, the Beijing silver medallist, appeared to back Pistorius on Wednesday, saying it was time to "re-evaluate the formula".

"All I know is that there is a maximum height. I think we need to come together and re-evaluate the formula and have an idea of the exact height for an athlete to run in or maybe have a variation in height of one cm, so you know you're racing the same athlete in all competitions," he said.

"As time changes science changes too, so we just have to make sure that it is fair to all competitors. Right now it's like (comparing) apples to oranges, not apples to apples."