US safety officials announced on Thursday that they had received more than 60 complaints from Toyota owners who were still experiencing sudden unintended acceleration even though their vehicles had been repaired by Toyota dealers.

The National Highway Traffic Safety Administration, which has come under pressure from Congress and consumer safety groups because of allegations that it responded too slowly to warnings of problems in Toyota vehicles, said it had the authority to order Toyota to “provide a different solution” if current efforts were not working.

“We are determined to get to the bottom of this,” said David Strickland, the NHTSA administrator.

The news marks yet another problematic development for Toyota, which is grappling with a massive vehicle recall, a loss of trust among consumers and a potential criminal investigation into its handling of safety issues.

The president of the company’s US operations admitted in testimony before Congress last month that Toyota’s recall may not completely solve problems of sudden unintended acceleration.

The Japanese carmaker was criticised by Henry Waxman, chairman of the House energy committee, among others, for not investigating thoroughly enough whether electronic failures were the source of the unexplained accelerations.

Toyota did not immediately comment on the NHTSA remarks.