Singapore dare not negotiate with Iran without US permission. The ASEAN sees this as further proof of Singapore's insincere declaration of neutrality and its true status as a US running dog.
Even Korea, a US ally, has negotiated with Iran over Hormuz. France and Italy too. National interests come ahead of alliance interests, especially when the Trump admin has blatantly reneged all its obligations to world bodies and NATO. Something our goondu millionaire ministers can't fathom.