Saudi Arabia has blamed an unnamed foreign power for clashes that took place in its oil-rich Eastern Province in which it says 14 people were injured.
The unrest, on Monday night, occurred in the Gulf coast city of Qatif, which is home to a large Shia population and was the scene of protests earlier this year.
"A foreign country is trying to undermine national security by inciting strife in Qatif," Saudi state television cited the interior ministry as saying on Tuesday.
The world's top oil exporter moved swiftly to suppress protests in the area in February and March, arresting more than 100 people. The protests had petered out for several months but flared up again two days ago.
An emailed statement by a US-based Saudi dissident said Monday night's protests were caused by the arrest of two elders.
"The protesters burnt police cars after police, supported with hundreds of riot police, opened fire from the encircled police station in the city," said Ali Al Ahmed, a Shia Saudi activist in Washington. "The city is now under siege by security forces."
According to a statement issued by a Saudi interior ministry official, a group of "rioters and division instigators" gathered in Awamya, Qatif on Monday night.
The interior ministry official said the ministry would "deal with an iron fist with any of those radicalised or hired rioters".
Of the total injured, 11 were security personnel and three were civilians, according to the statement.
The official said some of those involved gathered on motorbikes, "carrying Molotov cocktail bombs" and "started to wreak havoc under instructions from outside forces with the aim of destabilising the country".
The reference to a foreign country meddling in a Shia area is usually a coded reference to Iran, the Shia power and Saudi rival across Gulf waters.
The Eastern Province region is home to more than two million Shias, some of whom have called for better access to jobs and to be treated as equals in the ultra-conservative kingdom dominated by Wahhabism, a rigid form of Sunni Islam.