Singapore military took part in the Iraq War, Operation Enduring Freedom and Combined Task Forces 151. The latter battled and continues to battle Somali pirates in the Gulf of Aden.
Singapore’s lifeblood is trade. For the size of the country they have a HUGE military to defend such trade. You threaten a country’s lifeblood, you provoke a response. Sometimes, even less provokes a response. Just look at the Falklands War! Elements of the RSN have served in the Gulf of Aden, not too far from the Persian Gulf, so stationing RSN ships in the Gulf is not out of the question to protect their trade.
I seem to recall a certain minor power (at the time) doing something similar two hundred years ago. Are familiar with a certain song that carries the line “...to the shores of Tripoli.”?
They participated in those operations with heavy logistical support from other nations. Iran may have concerns about the reaction of certain nations, but I doubt Singapore is on the short list.
For years Jefferson tried to encourage the French, where he served as Ambassador, to help form a European coalition of forces to take on the Barbary Pirates. Finally, after one of our ships was captured and our citizens held for ransom, he acted for our country alone.