Malaysia has summoned Singapore's high commissioner over the alleged participation of three of the city-state's diplomats in a mass rally for electoral reform.
Malaysian Foreign Minister Anifah Aman said he summoned Ong Keng Yong Friday to explain that "the direct participation of diplomats in the illegal rally is an inappropriate move".
"I also stressed to Ong Keng Yong that the Ministry of Foreign Affairs would not hesitate to take stronger diplomatic actions against diplomats who are found to have stepped beyond the diplomatic norms," he said in a statement late Friday.
Tens of thousands rallied in the capital Kuala Lumpur on April 28 to call for electoral reforms, including a clean-up of the voter roll. Protesters clashed with police, who used tear gas and water cannon, and more than 500 people were arrested.
The Singapore High Commission denied that the diplomats participated in the rally, saying they attended as observers as part of their "diplomatic duties".
"The Singapore government does not interfere in any country's political processes," it said in a letter to Malay-language daily Utusan Malaysia published on its website.
Polls, expected to be fiercely contested, are due in the first half of next year, but Prime Minister Najib Razak is widely expected to call for elections before that.
Opposition leaders and activists say the electoral system is marred by irregularities and favours Najib's coalition, which has ruled the country since independence in 1957.
Malaysia and Singapore -- two former British colonies that separated in 1965 after a troubled union -- have had close ties in recent years and worked on resolving long-standing issues, such as land disputes.