(Reuters) -Japanese carmaker Toyota Motor (NYSE:TM) Corp has stopped sales of its Yaris Ativ, a senior official said on Monday, after its affiliate Daihatsu rigged part of the door in side-collision safety tests.

Speaking at a press conference in Bangkok, Toyota’s CEO for the Asia region, Masahiko Maeda, said the problem may have occurred due to pressure during the development of the Ativ model, adding that the vehicles customers were using were safe.

“If development had been carried out under appropriate conditions, this kind of problem would of course not have happened,” Maeda said.

“I think the fact that it still happened, means there was some kind of pressure at the development site,” he said, adding that the vehicle’s relatively large size may have posed a challenge to the development.

Toyota and Daihatsu disclosed last month they were investigating how part of the door in side-collision safety tests carried out for some 88,000 small cars, most of which were Ativs, had been changed for the purpose of side-on crash safety testing.

Thailand is Toyota’s fourth-biggest global centre by production volume after Japan, the U.S. and China. It produced some 659,000 vehicles, including models of its luxury brand Lexus, in the country last year.