RIYADH (AFP) - Saudi Arabia said on Saturday (June 27) three Iranian boats were "forced to retreat" from its waters after warning shots were fired, according to state media.

"At 6.30pm (local time) on Thursday... the coastguard spotted three Iranian boats after they entered Saudi waters," the official Saudi Press Agency reported.

The ships "refused to respond" to repeated warnings, after which "warning shots were fired... forcing them to retreat", it added.

The report did not identify what kind of ships they were.

Sunni powerhouse Saudi Arabia terminated diplomatic relations with Shi'ite-dominated Iran following 2016 attacks by protesters on its missions in Iran after Riyadh executed revered Shiite cleric Sheikh Nimr al-Nimr.

Saudi Arabia, the birthplace of Islam, has been at odds with Iran since the Islamic revolution of 1979 ushered in a Shi'ite theocracy and set the two countries on a collision course.

They today stand on opposing sides of conflicts in the Middle East, from Syria to Yemen.

Tensions have risen in the last year after a series of attacks on oil tankers in the Gulf and Saudi oil installations, incidents that roiled global energy markets last year.

Both the United States and Saudi Arabia have accused Iran of being behind those attacks, a charge denied by Teheran.