A Thai man suspected of killing a former Cambodian opposition lawmaker in Bangkok has confessed to the crime, police said Saturday.

"I confess that I did wrong," Ekkalak Paenoi said to police and media after being charged with premeditated murder and unauthorized gun ownership.

Lim Kimya, a former lawmaker for the dissolved Cambodia National Rescue Party (CNRP), was gunned down on Tuesday by a motorcyclist as he arrived in Bangkok by bus from Cambodia with his French wife.

Cambodian opposition figures have accused the country's powerful former leader Hun Sen of ordering the shooting.

Police in Cambodia said they arrested the suspect on Wednesday and took him to the Thai border following an extradition request.

He was picked up by a Thai police helicopter on Saturday and taken to Bangkok.

"We can't determine the motives yet, please give us time," said Somprasong Yenthuam, a senior police official.

Thai media have said Ekkalak was a former marine.

Yenthuam told reporters an arrest warrant for a Cambodian accomplice had also been issued.

A Cambodian government spokesman denied official involvement in the slaying.

Scores of Cambodian opposition activists have fled to Thailand in recent years to avoid alleged repression at home. Some were arrested and deported back to the country. 

Hun Sen ruled Cambodia with an iron fist for nearly four decades, with rights groups accusing him of using the legal system to crush opposition to his rule.

He stepped down and handed power to his son Hun Manet in 2023, but is still seen as a major power in the kingdom.

France has condemned the killing of Lim Kimya, who also held French citizenship.