The republic's foreign minister says that they did not wear yellow shirts or take part in any demo.
Foreign Minister K Shanmugam told parliament that diplomats from the Singapore High Commission were at the April rally as “impartial observers” along with counterparts from more than 10 countries.
“Our officers were doing their duty. They were there as observers,” Shanmugam said in parliament in reply to a question from a lawmaker.
“They did not wear yellow shirts or take any action to affiliate themselves with any political entity,” he said.
Last month, Malaysia summoned Singapore’s high commissioner over the alleged participation of the diplomats in the April 28 rally.
Tens of thousands of protesters, most of them wearing symbolic yellow shirts, gathered in the Malaysian capital 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.
Shanmugam said the allegation was unlikely to affect ties, which have improved markedly in recent years after both sides worked on finding ways to resolve long-standing issues such as land disputes.
“We have all worked hard to build up the strong ties that we currently enjoy,” said Shanmugam.
“Neither of us has an interest in undermining the relationship in this way.
“Relations between Singapore and Malaysia have always been bigger than any specific disagreements or points of contention.”