Saudi Arabia's Islamic Affairs Ministry is investigating 17 mosque imams in the capital Riyadh for not using their Friday sermons to denounce an Al Qaeda attack this month, the English daily Arab News reported on Saturday.

The kingdom has kept a close eye on mosque sermons for evidence of militancy since last decade, when Al Qaeda staged a series of attacks inside Saudi Arabia that killed hundreds.

Arab News cited Tawfiq Al-Sudairi, an under-secretary at the Islamic Affairs Ministry, as saying the imams were under investigation "for allegedly failing to highlight the incident in their sermons".

Al Qaeda in the Arabian Peninsula (AQAP) raided Sharurah, a small Saudi frontier town, from its base in Yemen early this month, killing four border guards and another Saudi citizen before all the attackers were killed or injured.

The attack was the militant group's first inside the kingdom since 2009 when it attempted to assassinate Prince Mohammed bin Nayef, who was then the kingdom's security chief but is now interior minister.

On Friday, the Interior Ministry said its infrastructure facilities were secure after local media reported that an Iraq-based militant had warned his family to leave their homes because of a planned attack on the kingdom.

The ministry's spokesman was quoted in Arab News as saying those reports were incorrect, but that security had been strengthened around all strategic facilities due to the chaos in Iraq. - Reuters