Slogans against the royal family have been daubed on walls in the eastern Saudi Arabia, the scene of deadly clashes with security forces, an AFP photographer said Friday.

The Al-Saud ruling family must be “held responsible for the blood of the martyrs”, “Down with Mohammed bin Fahd” bin Abdul Aziz, the governor of the kingdom's Eastern Province, were painted in the streets of the city of Qatib.

Security forces were posted at entrances to Qatib and conducting patrols, although no incidents were reported during a visit organized by Saudi authorities for journalists based in Riyadh.

According to the authorities and medical sources, four people were shot dead in unrest since Sunday in the mainly Shiite eastern region of the predominantly Sunni Muslim kingdom.

Prince Mohammed bin Fahd has vowed that the interior ministry will probe the deaths.

On Friday, clerics called at weekly prayers for the authorities to come forward with conciliatory gestures towards their community, who often complain of being marginalized in the oil-rich Persian Gulf state.

“The government is called upon to make a gesture of appeasement to ending discrimination so as to heal the wounds,” said Sheikh Hassan Saar, as fellow cleric Hassan Nimr urged authorities “not to doubt the loyalty of Shia Muslims.”

However, Saudi Arabia's mufti, Sheikh Abdul Aziz al-Sheikh, quoted in Okaz newspaper, charged that “the troublemakers of Qatif belong to a gang which takes its orders from abroad”.