Saudi Arabia said Monday it had seized weapons from a boat captured after the navy fired warning shots at vessels approaching a Gulf oil platform, at a time of tensions with Iran and Qatar.

Three small boats entered Saudi territorial waters at about 8:30 pm on Friday and "headed at speed towards platforms of (the) Saudi oil field of Marjan", a government statement said.

Saudi naval forces fired warning shots at the boats, which were carrying "red and white flags", and captured one of the vessels but two escaped, the statement added.

The seized boat was "loaded with weapons for subversive purposes", it said, but gave no details.

The statement came two days after Iran accused Saudi Arabia of shooting and killing one of its fishermen.

Iran said it was investigating the Saturday shooting, after two fishing boats may have strayed into Saudi waters.

Majid Aghababaie, head of border affairs at Iran's interior ministry, said one of the boats was missing after the Saudi coastguard opened fire on the vessels, which had drifted due to high waves.

Aghababaie said "even if the boats had entered Saudi waters, the coastguard were not authorised to open fire".

Saudi Arabia regularly accuses Shiite-dominated Iran of interfering in Middle Eastern countries, and has suggested it is linked to instability in the kingdom's east, where minority Shiites live.

Saudi Arabia, the United Arab Emirates, Egypt and others severed diplomatic and economic ties with Qatar two weeks ago, accusing Doha of supporting groups, including some backed by Iran, "that aim to destabilise the region".

Qatar denies any such support for extremists.

Source: AFP