US Congressman Tony Gonzales has admitted to having an extra-marital affair with an aide, having previously denied that the relationship ever happened.

The Texas Republican, who is married with six children, said the relationship with married staff member Regina Santos-Aviles, who died by suicide last year, was a “mistake” and a “lapse in judgement”. “I take full responsibility for my actions,” Gonzales, 45, told a podcast.

His admission came hours after a House of Representatives panel launched an ethics investigation into the relationship, and ahead of a primary run-off election. Gonzales had previously dismissed the allegations as “blackmail” and a “co-ordinated” attack to unseat him.

Gonzales was endorsed by US President Donald Trump before the affair allegations surfaced.

The lawmaker is now facing growing calls for his resignation, including from fellow Republicans. Among them are South Carolina Congresswoman Nancy Mace, who has accused him of “predatory behaviour”.

On Thursday, the Republican leadership in Congress said that Gonzales should end his campaign for re-election.

Gonzales told conservative podcaster Joe Pags in an interview released on Wednesday that Santos-Aviles’ death had nothing to do with the affair, saying she was “thriving” at work.

“I had absolutely nothing to do with her tragic passing,” he said. “And, in fact, I was shocked just as much as everyone else.”

The House Ethics Committee announced on Wednesday that it was launching an investigation into whether Gonzales “engaged in sexual misconduct” towards one of his employees.

The panel will also examine whether he discriminated unfairly by “dispensing special favours or privileges”.