PHNOM PENH (AFP) - Cambodia's Prime Minister Hun Sen vowed on Monday (Dec 28) to create a new law banning political party leaders from holding dual nationality, a move targeting his arch-rival, who has fled overseas.

The nation has been plunged into a political crisis after an arrest warrant was issued last month for Mr Sam Rainsy - the most prominent opposition leader - who has a Cambodian and a French passport.

He fled to France, declaring the charges against him were politically motivated.

Mr Hun Sen said the new law would be passed next year and affect political party leaders and people holding positions in some key institutions, requiring them to hold only Cambodian nationality.

"In the future the law on political parties must limit the leader of political parties to hold only Cambodian nationality so that such people cannot use a foreign passport to flee when there is a problem," he said at a graduation ceremony.

"If you have a foreign nationality, you must quit it. Don't be afraid of giving up a nationality in order to serve Cambodia," he said.

Mr Hun Sen has ruled Cambodia with an iron fist for the last 30 years and opposition parties rarely succeed in halting or amending the ruling party's proposed laws.

Mr Rainsy has gone into self-imposed exile three times to avoid imprisonment and faces a string of charges, including one for defamation.

Mr Hun Sen also pledged that he would not seek a royal pardon for his rival.

"If I sign for the third time (to ask for a royal pardon for him), I will cut my right arm off," he said, calling on Mr Rainsy to return and serve the jail term.