UKMTO received a report of an incident approximately 50 nautical miles (93 km) west of Yemen's Hodeidah, which authorities were investigating, it said in an advisory note.
Ambrey received reports of suspicious activity from two merchant vessels southwest of Yemen's Mokha, though no damage was reported.
A tanker either saw flares or missile trails, while a bulk carrier detected three small vessels approximately 1 mile in the direction of their port quarter, Ambrey said in an advisory note.
The bulk carrier reported seeing two missiles fired from the direction of the boats and one unmanned aerial vehicle flying ahead of the vessel, Ambrey added.
"Ambrey assessed this event was separate from an event that was reported west of Hodeidah around the same time," it said.
Yemen's Iranian-backed Houthi militants, who control much of Yemen, have launched wave after wave of exploding drones and missiles at commercial vessels since Nov. 19, in what they say is a protest against Israel's military operations in Gaza.
Ansarullah, a Houthi group, targeted a vessel in the Red Sea, a Yemeni military source told Al Jazeera on Tuesday.
The Houthi campaign has been extraordinarily disruptive to international shipping, causing some companies to suspend transits through the Red Sea and instead take the much longer, costlier journey around Africa.
(Reporting by Enas Alashray and Adam Makary; Editing by Sonali Paul)
