Singapore is "concerned and disappointed" after the two men appeared at the event in Jakarta this week dressed as Indonesian marines Usman Haji Mohamed Ali and Harun Said, who were executed for the bombing, the foreign ministry said in a statement late Thursday.

Three people were killed and 33 others injured in the bombing of MacDonald House, downtown Singapore, in March 1965.

The attack was part of efforts by then Indonesian president Sukarno to stage an armed confrontation against the newly formed federation of Malaysia, which included Singapore. The two marines had been ordered to infiltrate Singapore and carry out the attack.

Navy spokesman Untung Suropati described the two marines as "heroes" who should serve as role models for young Indonesians.

"Usman and Harun are our heroes, and it was an international expo with a young generation of the military and students visiting," he told AFP in Jakarta.

"We need to show them we have great heroes in the hope that they can be role models for them."

Singapore said a delegation from its armed forces had pulled out of the Jakarta International Defence Dialogue (JIDD) exhibition on Wednesday after learning of the stunt, while diplomats from its embassy in Jakarta have spoken with officials there "to express disappointment".

The two marines had been stationed at the navy's stall at the JIDD dressed in vintage uniforms and purple berets, with "Usman" and "Harun" on their name tags.

Indonesia had already outraged Singapore last month by naming a newly refurbished navy frigate "Usman Harun" in honour of the marines. The ship has been banned from Singaporean ports and naval bases.

Relations between the two countries hit a low point in the late 1990s after the fall of former dictator Suharto, and his successor B.J. Habibie famously referred to the tiny city-state as a "little red dot" on the map.

But ties have improved considerably in recent years, and Indonesia is now Singapore's third largest trading partner.