By Shabtai Gold, dpa (TNS)

RIYADH, Saudi Arabia — A suicide bomber killed 19 people during Friday prayers at a Shiite mosque in eastern Saudi Arabia, residents and officials said, raising fresh concern about sectarian strife in the kingdom.

Around 100 people were injured in the attack, according to Saudi-owned broadcaster Al Arabiya.

The suicide bomber apparently had an explosives belt that he detonated in the mosque in al-Qadaih village, in the Qatif region, according to Interior Ministry spokesman Mansour al-Turki.

Residents described emergency crews working at the blood-soaked site of the attack, which took place on the birthday of Husayn ibn Ali, a figure from the 7th century who is revered by Shiites.

There were tense scenes on the streets of the region, with angry crowds protesting against the attack, according to residents.

Videos posted on social media by local people showed crowds chanting Shiite slogans.

The government pledged to find the perpetrators of the attack.

In November, seven Shiites were killed in a shooting attack, which Saudi security forces blamed on the Islamic State Sunni extremist group. Four alleged masterminds were arrested.

There have long been tensions between the Shiite minority in Saudi Arabia and the government of the Sunni kingdom, including crackdowns on residents of the oil-rich region, who say they are victims of discrimination.

Sectarian tensions are also being fuelled by the Saudi-led military campaign in Yemen against the Shiite Houthi rebels.

The Saudi monarchy adheres to the Wahhabi doctrine, a strict form of Sunni Islam.

(c)2015 Deutsche Presse-Agentur GmbH (Hamburg, Germany)

Photo: An entrance to a mosque in Riyadh. Edward Musiak via Flickr