Attack on Shias fans fears of jihadi blowback in Sunni Saudi Arabia Fears of jihadi "blowback" from the wars in Syria and Iraq reaching Saudi Arabia have been fanned by a deadly sectarian attack that killed five people on the Shia religious holiday of Ashura. Saudi police on Tuesday announced the arrest of nine people suspected of involvement in what was labelled a "terrorist" shooting at a Shia mosque in al-Ahsa in the country's eastern province, as mainstream Sunni clerical leaders condemned the incident, which analysts have described as ominous. Al-Arabiya TV described the 10-strong group of attackers as Saudi nationals led by a man who had fought in Iraq and Syria. Reports from Riyadh said three masked assailants fired machine guns and pistols at random on a crowd leaving a Husseiniya (place of worship) in the village of al-Dalwa on the eve of the festival on Monday. Five people were killed and nine injured. Videos purporting to show the aftermath of the attack showed a body lying in a pool of blood outside a building, with people milling around and calling for help. Al-Arabiya reported later that a security officer and a wanted man had been killed in Qasim province - an incident it said was linked to the al-Ahsa attack. Further arrests were expected, it said. The fear is that the Sunni-Shia tensions unleashed by the war in Syria and the rise of the Sunni jihadis of Islamic State (Isis) now pose a real security threat inside the conservative kingdom - just as the fighters returning from the Saudi-backed anti-Soviet war in Afghanistan, later to make up al-Qaida, were seen as "blowback" against the ruling Al Saud dynasty. Saudi Arabia has been blamed for the rise of Isis by funding armed Islamist groups fighting to overthrow President Bashar al-Assad while thousands of its nationals have fought in Syria and Iraq, many encouraged by extremist clerics who stir up sectarian hatred. In recent months however it has imposed stricter controls and criminalised fighting abroad while also announcing scores of arrests. "There has never before been a "successful" terrorist attack against Shia in eastern Saudi, even though there were plots," said Toby Matthiesen of Cambridge University, an expert on the Gulf. It means the sectarian conflict in the region has now definitively spilled over into Saudi Arabia. Fahad Nazer, a US-based terrorism analyst, said on Twitter there was "little doubt that the target, method and timing of the attack are all ominous signs." Ashura commemorates the death of Imam Hussein, the grandson of the prophet Muhammad, at the battle of Karbala (in present-day Iraq) in the seventh century. The subsequent schism in Islam has been an ugly feature of the Arab spring, especially in Iraq, Syria and Bahrain, with Sunni Saudi Arabia locked in competition with Shia Iran - their strategic interests overlaying sectarian animosity. Protests and sporadic attacks on security forces have racked Shia areas of the oil-rich eastern province, where the minority community complains of marginalisation and discrimination. Shia Muslims make up less than 15% of Saudi Arabia's 20 million population. Longstanding tensions escalated last month after a court handed down a death sentence against the country's leading Shia cleric, Nimr al-Nimr, a driving force behind anti-government demonstrations in 2011. Iran has urged the Saudis not to carry out the sentence. On Tuesday Iranian Arabic-language media also described the al-Ahsa incident as an attack by the Saudi authorities. But comments on Saudi social media urged Saudis to reject sectarianism while the shootings were quickly condemned as a "heinous crime" by the council of senior religious scholars as well as government officials. "With the execution of Nimr al-Nimr looming, and this coming on the eve of Ashura, it is a very bad and worrying sign," Matthiesen added. But there are also encouraging signs of many Sunnis denouncing the attacks.