Masked men threw firebombs at an intelligence service compound in the city of Qatif in eastern Saudi Arabia, reports said on Monday.

A Saudi Interior Ministry spokesman said "there was a failed terrorist attempt to burn the building with Molotov cocktails" and that one of the assailants was captured.

Video footage posted on social media and dated January 9 showed several masked young men moving under cover of darkness and lobbing firebombs over the protective outer wall of a building compound. Most of the firebombs were seen exploding on the ground inside, setting a nearby tree on fire.

The authenticity of the footage could not immediately be confirmed.

It was not initially clear who was behind the attack. But the recording contained a footnote indicating that it was carried out by Shi'ite youth seeking to avenge the execution of Sheikh Nimr Al-Nimr, convicted of sedition and rioting. - Reuters