The massive Ras Tanura refinery on Saudi Arabia's Gulf coast went into partial shutdown on Monday after the strike by two drones, three days into the Middle East war.

"It depends if this is seen as a direct attack on Aramco by the Iranian leadership or a rogue drone that just came close," the source told AFP, referring to the giant state oil company.

"At this stage I think Saudi will watch and wait."

Military retaliation would be a possible option if Iran were seen as launching a targeted campaign against the kingdom's oil installations. Saudi Arabia is the world's biggest oil exporter.

Saudi Arabia would target "Iranian oil facilities if Iran mounts a concerted attack on Aramco", the source said.