Saudi Arabia says that it captured three members of Iran's Islamic Revolutionary Guards Corps (IRGC) aboard a boat approaching the kingdom's offshore Marjan oil field.
The three "are now being questioned by Saudi authorities," the Information and Culture Ministry said in a statement on June 19, amid heightened tensions between the two countries.
The vessel, seized by the Saudi Navy on June 16, was carrying explosives and intended to conduct a "terrorist act" in Saudi territorial waters, the statement said.
Saudi media earlier said that the navy had fired warning shots when three small boats entered Saudi territorial waters and headed at high speed toward the platforms.
Iran, however, accused Saudi border guards of opening fire on an Iranian fishing boat, killing a fisherman. Iran’s Tasnim news agency said on June 17 that the boat was one of two Iranian boats fishing in the Persian Gulf that had been pushed off course by waves.
An Iranian ministry of interior official also said on Monday that Saudi Arabia's claim that it had detained three members of the Iranian military was not correct, according to a report by the Young Journalists Club news site.
"The people who came face to face with the powers of (Saudi Arabia) were simple fishermen who had fishermen boats," Majid Aqababai, the director general of border affairs at the interior ministry said, according to the Young Journalists Club site.
Tensions between the two regional rivals have steadily deteriorated. On June 5, Saudi Arabia and other Arab governments severed ties with Qatar, citing its support of Iran as a reason.
Days later, twin terror attacks claimed by the extremist group Islamic State (IS) killed at least 17 people in Tehran. Iran repeated accusations that Saudi Arabia funds Sunni Islamist militants, including IS.
Riyadh has denied involvement in the attacks.