British maritime authorities said on Friday they were investigating a report of an incident 50 nautical miles north of the Yemeni port of Mokha near the Bab al-Mandab Strait at the southern end of the Red Sea.
The United Kingdom Maritime Trade Operations (UKMTO) agency said it had also received reports of an incident around 60 nautical miles southwest of Hodeidah, another Yemeni port. It was not immediately clear whether the incidents were related.
The UKMTO advised ships to transit with caution and report any suspicious activity, but did not immediately provide further details about the incidents.
Yemen's Iran-aligned Houthis have attacked vessels in Red Sea shipping lanes and fired drones and missiles at Israel since the start of the Israel-Hamas war in Gaza over two months ago, heightening fears of a wider conflict in the Middle East.
The Houthis, who rule much of Yemen, says their attacks are a show of support for the Palestinians and has vowed they will continue until Israel stops its offensive in Hamas-ruled Gaza .
Late on Thursday, the Houthis claimed to have carried out a military operation against a Maersk container vessel, directly hitting it with a drone. The Danish shipping company denied the claim and said the vessel was not hit.
Reporting by Nadine Awadalla and Tala Ramadan; Editing by Christopher Cushing and Mark Heinrich