Gunmen shot dead two Saudi Arabian security personnel in the kingdom's eastern city of Dammam, signalling that unrest in Shia-dominated areas of the country has legs.
The police officers were killed in the al-Dhabab neighborhood of Dammam late on Monday night, according to local reports.
One of the officers was driving back home after his duty hours when the assailants opened fire, Al Arabia reported.
"Two security men were martyred ... three unidentified gunmen opened fire on the two security men as they returned from work in Dammam," the report said.
The Saudi Press Agency said the attackers were not identified. The policemen came under "heavy fire from an unknown source" the state news agency said.
Two police officers were shot dead in September in Dammam, the capital of the Sunni kingdom's eastern province. Sunni--ruled Riyadh has tight grip on the Shia dominated regions in the kingdom, but unrest among the Shia minority has been worsening in recent years.
However, Saudi Arabia has attributes the recent surge in attacks on its security forces to the rise of Islamic State-led Sunni militants, or Daesh, in the region.
In January Saudi Arabia executed 47 al-Qaeda linked prisoners including many Shiite leaders on terror charges. The execution of prominent Shi'ite cleric Nimr al-Nimr triggered severe unrest in the Qatif district in the eastern province of the country.
In June, at the end of Ramadan, a series of terror attacks hit Saudi Arabia within in 24 hours, including in the holy city of Medina, killing four people.