DUBAI - British security firm Ambrey said on Friday merchant vessels transiting the Gulf and Western Indian Ocean were advised to stay alert in case of increased uncrewed aerial vehicle (UAV) activity in the region.

Ambrey said it had received information that indicated an "Israeli military strike" was conducted on Isfahan, Iran.

Earlier, the United Kingdom Maritime Trade Operations (UKMTO) agency said it had seen similar reports but that there were no indications commercial maritime vessels were the intended target of the strike.

Oil prices jumped as high as $3 a barrel on Friday in reaction to reports of the strike, sparking concerns that Middle East oil supply could be disrupted. Brent crude gave up some of those gains, trading up 1.85% at $88.74 at 0551 GMT after reaching a high of $90.75.

Israel has attacked Iran, three people familiar with the matter said. Iranian state media reported early on Friday that its forces had destroyed drones, days after Iran launched a retaliatory drone strike on Israel.

Iran's Fars news agency reported three explosions were heard near an army base in the central city of Isfahan. An Iranian official told Reuters there was no missile attack and the explosions were the result of the activation of Iran's air defence systems.

(Reporting by Nadine Awadalla and Clauda Tanios; Editing by Michael Georgy and Christopher Cushing)