RIYADH, Saudi Arabia -- Saudi Arabia announced Saturday it has broken up planned Islamic State attacks in the kingdom and arrested more than 400 suspects in an anti-terrorism sweep, a day after a powerful blast in neighbouring Iraq killed more than 100 people in one of the country's deadliest single attacks since U.S. troops pulled out in 2011.
The Saudi crackdown underscores the OPEC powerhouse's growing concern about the threat posed by the Islamic State group, which in addition to its operations in Iraq and Syria has claimed responsibility for recent suicide bombings aimed at Shiites in the kingdom's oil-rich east and in next-door Kuwait.
The Saudi Interior Ministry accused those arrested over the "past few weeks" of involvement in several attacks, including a suicide bombing in May that killed 22 people in the eastern village of al-Qudeeh. It was the deadliest militant assault in the kingdom in more than a decade.
It also blamed them for the November shooting and killing of eight worshippers in the eastern Saudi village of al-Ahsa, and for behind another attack in late May, when a suicide bomber disguised as a woman blew himself up in the parking lot of a Shiite mosque during Friday prayers, killing four.
The Interior Ministry said that in June they thwarted a suicide bomb attack on a large mosque in eastern Saudi Arabia that can hold 3,000 worshippers, along with multiple planned attacks on other mosques and diplomatic and security bodies.
Those arrested included suspects behind a number of militant websites used in recruiting, the ministry said.
Saudi Arabia branded the Islamic State group a terrorist organization last year and has joined the U.S.-led coalition targeting it in Syria and Iraq. Authorities have vowed to punish those responsible for terrorist attacks inside the kingdom, the Arab world's largest economy.
Dubai-based geopolitical analyst Theodore Karasik said the arrests are aimed at part on reassuring the country's Shiite minority, who long have complained of discrimination in the kingdom, which is governed by an ultraconservative interpretation of Sunni Islam.
"It sends a message that the Ministry of Interior is not losing a grip and wraps up the potential nodes of Daesh recruits in the kingdom," he said, using an alternate name for the group.
In Iraq, authorities said at least 115 people, including women and children, were killed in Friday night's attack on a crowded marketplace in Iraq's eastern Diyala province. The mostly-Shiite victims were gathered to mark the end of the Islamic holy month of Ramadan, which ended Friday for Iraqi Shiites and a day earlier for Iraqi Sunni Muslims.
Police said a small truck detonated in a crowded marketplace in the town of Khan Beni Saad. At least 170 people were wounded in the attack, police officials said, speaking anonymously because they are not authorized to brief journalists.
The Islamic State group claimed responsibility for the attack in a statement posted on Twitter accounts associated with the militants.
Iraq's speaker of parliament, Salim al-Jabouri, said Saturday that the attack has struck an "ugly sectarian chord," and added that government is making "attempts to regulate Daesh's terror from destabilizing Diyala security."
A number of towns were captured by the extremists in the province last year. Iraqi forces and Kurdish fighters have since retaken those areas, but clashes between the militants and security forces continue.
Security forces were out in full force across Diyala on Saturday, with dozens of new checkpoints and security protocols immediately put in place.
The Islamic State group holds about a third of Iraq and Syria in a self-declared "caliphate." The U.S.-led coalition airstrikes have not stopped the group from making advances.
Diyala, which borders Iran, is the only province in Iraq where Iranian jets are known to have conducted airstrikes against the Islamic State group earlier this year.
Elsewhere in Iraq, a roadside bomb on a commercial street in Baghdad's Dora district Saturday killed four people and wounded seven. North of Baghdad, a roadside bomb on a commercial street in al-Rashidiya killed three people and wounded 11.
Meanwhile, reports emerged Saturday that the Islamic State group used projectile-delivered poison gas against Kurdish forces in Iraq and Syria on several occasions last month.
Joint, on-site investigations by two U.K.-based organizations -- Conflict Armament Research and Sahan Research -- concluded that Islamic State forces used chemical agents delivered through what appears to be locally manufactured shells to attack Iraqi peshmerga forces and Syrian Kurdish People's Protection Units, also known as the YPG, on June 21, 22 and 28.
"The three attacks are the first documented use by IS forces of projectile-delivered chemical agents against Kurdish forces and civilian targets," the report said.
In the Syria attacks, Islamic State militants launched 17 artillery projectiles against YPG forces stationed to the south of the village of Tell Brak in Hassakeh province. The projectiles released a chemical agent which induced in some cases loss of consciousness and temporary, localized paralysis. Twelve YPG personnel were hospitalized. Another seven projectiles were also launched into civilian residential areas in Hassakeh.
In the Iraq attack, Islamic State forces fired a projectile containing a liquid chemical agent at a peshmerga checkpoint near the Mosul Dam, triggering symptoms among the Iraqi forces that included headaches, nausea and light burns to the skin.
The findings on the attacks in Syria were confirmed by an YPG statement issued Saturday. The exact type of chemical used is not known.
"Although these chemical attacks appear to be test cases, we expect IS construction skills to advance as rapidly as they have for other (bombs)," said Emmanuel Deisser, Sahan's managing director.
