Prime Minister Prayut Chan-o-cha has insisted that any police officers involved in extorting money from a Taiwanese actress during her trip to Thailand early this month must face legal action.

Prayut said any problem involving police extorting money from tourists must be fixed and rogue officers punished.

"There are still a lot of decent police officers, but we must get rid of rogue ones,'' the prime minister said.

The actress, Charlene An, complained via social media that she was stopped by police at about 1am on Jan 4. She claimed she was kept there for two hours, and finally learned she had to pay for her freedom. She said she paid 27,000 baht and was freed.

The national police chief apologised to people affected by the actions of police on duty at the time.

Police investigators may go to Taiwan and Singapore to question people involved, he said.

He said police involved in the alleged extortion admitted only to their failure to charge the actress for having an illegal vaping device. However, the officers denied they extorted 27,000 baht in exchange for her freedom on Jan 4.

A source said 14 officers were questioned over the case on Monday, and all denied taking bribes.

Seven officers at Huai Khwang station were transferred to inactive posts.

The actress posted on her Instagram account on Tuesday, expressing her gratitude to those who had given her encouragement, support and care "to help me walk through this moment of traumatic darkness".