A former Cambodian opposition MP was shot dead by a gunman on a motorcycle in Bangkok on Tuesday, Thai media reported.

"Lim Kimya... died at the scene. Officers with the Metropolitan Police Bureau have launched a manhunt for the assassin," the Bangkok Post reported, adding that the deceased was a dual Cambodian-French national.

Thai police confirmed the death of a Cambodian man without identifying Lim Kimya, telling AFP "we are currently investigating the motives and will provide more information at a later time".

Multiple Thai media outlets reported that a gunman on a motorcycle opened fire on Lim Kimya as he arrived in the Thai capital from Cambodia's Siem Reap city by bus accompanied by his French wife and a Cambodian uncle.

An AFP photojournalist saw blood at the scene near the popular Khao San Road area of Bangkok.

Lim Kimya was elected as an opposition member of Cambodia's parliament following a general poll in 2013 in which the ruling party under former leader Hun Sen almost lost the election to its then-rival the Cambodia National Rescue Party.

The CNRP, which was founded in 2012 by opposition leaders Sam Rainsy and Kem Sokha, was dissolved by court order in 2017.

Scores of opposition politicians and MPs, including Lim Kimya, were banned from political activities following the party's dissolution.

Rights groups have accused Hun Sen -- who ruled Cambodia for nearly four decades -- of using the legal system to crush any opposition to his rule.

Scores of opposition politicians and activists were convicted and jailed during his time in power.

Despite holding French citizenship, Lim Kimya did not join the dozens of MPs who fled abroad after CNRP president Kem Sokha was detained on treason charges in 2017.

Lim Kimya told AFP at the time in Phnom Penh: "I will never give up politics".

His fatal shooting comes the same day Cambodia's influential former leader Hun Sen called for a new law to label anyone who attempts to topple his son Hun Manet's government as "terrorists".

Hun Sen stepped down in 2023 and handed leadership over to his eldest son, Hun Manet.