Saudi officials say a "booby-trapped boat was dealt and destroyed" off the coast of Yanbu port but according to two private maritime security firms a ship might have been "attacked".
A remotely piloted boat packed with explosives has targeted the Saudi port of Yanbu in the Red Sea, the kingdom said, with the blast sending black smoke into the sky off the coast.
Saudi Arabia claimed to have intercepted and destroyed the attack boat on Tuesday. However, private security firms suggested commercial traffic near the port may have been hit in the assault.
"A bomb-laden unmanned (vessel) was intercepted and destroyed this morning," Saudi Defence Ministry said in a statement, published by the official Saudi Press Agency.
"Naval units were able to detect and monitor the activity of the bomb-laden (boat) in the Red Sea waters off the shores of Yanbu."
Details remained scarce, but the incident comes after a series of attacks on shipping in the wider Mideast region amid a shadow war between Iran and Israel and against the backdrop of ongoing negotiations between Tehran and world powers over Iran's tattered nuclear deal.
The incident also comes amid the kingdom’s years-long war against Yemen’s Houthi rebels.
However, the rebels did not immediately claim any assaults on Tuesday and did not respond to a request for comment.
The state-run media quoted Saudi military spokesman Colonel Turki al Maliki saying the port was targeted by the drone boat.
"The booby-trapped boat was dealt and destroyed according to the rules of engagement," the report quoted al Maliki as saying, without providing evidence to support his claim.
The United Kingdom Maritime Trade Operations, run by the British navy, simply said it was "aware of reports of an incident" and that investigations were ongoing.
Private maritime security firm Dryad Global said it had reports that a ship had been "attacked," without elaborating.
Maritime security firm Neptune P2P Group reported that black smoke was seen billowing near the south entrance of the Yanbu port.
British maritime security firm Ambrey reported an "incident" off western Saudi Arabia, between the ports of Yanbu and Rabigh.
Earlier on Tuesday morning, smoke was seen rising from a vessel off the Saudi oil-shipping port of of Yanbu, the firm said.
Multiple tankers remain anchored or drifting in the area.
Yanbu port control broadcast a message by marine VHF radio, warning vessels to increase their level of alertness and monitor for any suspicious activity, Ambrey said.
The US Navy’s Mideast-based 5th Fleet declined to immediately comment on the incident.
Yanbu, 870 kilometres west of Riyadh, serves as the end point of the kingdom's crucial East-West Pipeline.
It allows crude oil pumped in its eastern fields to be shipped directly via the Red Sea, avoiding the Persian Gulf's chokepoint at the Strait of Hormuz.
Yanbu is also home to an oil refinery that can process 400,000 barrels of crude per day.
Fighting escalates in Yemen
The incident comes as fighting escalates in neighbouring Yemen between Saudi-backed government forces and Iran-aligned Houthi rebels.
Houthi insurgents are ramping up a bloody offensive to seize the oil-rich Marib region, the Yemeni government's last stronghold in northern Yemen.
The Houthi, who are battling the Saudi-led military coalition that intervened in Yemen's war in 2015, have also stepped up drone and missile strikes on Saudi targets, including its oil facilities.
The rebels have used bomb-rigged boats in the past to target the kingdom.
Last week, Greece said it will transfer a Patriot missile battery to Saudi Arabia to protect its critical energy infrastructure, as the Gulf kingdom grapples with the growing attacks.