Six small craft approached a merchant vessel about 50 nautical miles from the Yemeni city of Mocha on Saturday before leaving the area, the United Kingdom Maritime Trade Operations (UKMTO) organization said.
"The vessel and crew were reported safe," UKMTO added in an advisory note on the incident.
Yemen's Iranian-backed Houthi militants have stepped up attacks on commercial vessels in the Red Sea in protest against Israel's war in Gaza. Various shipping lines have suspended operations, instead taking the longer journey around Africa.
Drone launched from Yemen, shot down by US ship
A drone launched from Yemen was shot down in self-defense by a US ship in the southern Red Sea on Saturday in the vicinity of several commercial vessels, the US Central Command (CENTCOM) said in a statement.
The Houthis have vowed to continue attacks until Israel halts the conflict in Gaza, and warned that it would attack US warships if the militia group itself was targeted.