Shi'ite Muslim clerics in Saudi Arabia have criticised a religious edict from Sunni Muslim counterparts branding them infidels, saying that its authors were suffering from psychological problems.

A group of 22 hardline Sunni clerics last month said the Shi'ite branch of Islam was having "infidel precepts". The statement came after Lebanon's Shi'ite Hezbollah movement routed supporters of the Sunni-led government in the Lebanese capital.

The edict by representatives of the conservative wing in the official Sunni religious establishment was seen by some observers as a shot against King Abdullah's plan to set up a dialogue between Muslims, Jews, Christians and other faiths.

A conference with the king and Vatican officials in attendance is set for Madrid this month.

The government is also alarmed about the increased political power of Shi'ites in Iraq and Lebanon and Shi'ite dissidents hold out few hopes for the interfaith project.

The edict was the latest in a series of statements against Shi'ites since sectarian tension dragged Iraq to the brink of civil war in 2006 and Iranian-backed Hezbollah began mobilising opposition to the Sunni-led government in Lebanon.

A prominent Sunni Muslim Saudi cleric met with minority Shi'ite Muslim leaders last month in an attempt to soothe anger over the edict.

Saudi clerics, who adhere to an austere Sunni school often termed Wahhabism, have traditionally viewed Shi'ism as a heresy. But many government-allied clerics have toned down anti-Shi'ite rhetoric as King Abdullah has promoted "moderation".

"This sharp tone and discordant voice suffers from psychological complexes and has adopted confrontation and insults as its policy," 85 Shi'ite clerics and community leaders said in an unusual riposte.

"It is this voice that is responsible for the bloody scenes and incidents that have shaken this country," said the statement, referring to a campaign to destabilise the Saudi government launched by al Qaeda sympathisers in 2003.

"We ask our brothers who have wronged us with their fatwas (religious edicts) branding Muslims as infidels to reconsider and re-read the contemporary Shi'ite reality in a responsible manner," said the statement that was sent to Reuters.