Saudi security forces opened fire on protesters in the Eastern Province Shiite region of Al-Qatif on Monday, wounding several people, witnesses said.
The demonstrators had taken to the streets in the town of Shwika to protest against the death overnight Sunday of a 19-year-old Shiite man, Nasser al-Mheishi, accusing police of killing him, the witnesses said.
Mheishi had been wounded near a police checkpoint in unclear circumstances.
"The police told us that gunmen had opened fire on the police checkpoint... and that my son was caught in the crossfire between the police and the armed men, and was struck by four bullets," the man's father, Ali al-Mheishi told AFP.
But a witness later said that one of the policemen at the checkpoint shot Mheishi dead, his father said.
A police spokesman in the Eastern Province declined to comment.
According to militants the death is the second in the past few days after another young man was shot by security forces in the Shiite town of Awamiya.
In October 14 people, including 11 policemen, were wounding during clashes in Awamiya between security forces and demonstrators.
At the time the interior ministry in the Sunni-ruled kingdom blamed "outlaws" for the violence.
The group carried out acts causing "insecurity with incitement from a foreign country that aims to undermine the nation's security and stability," a ministry spokesman said in an indirect reference to Shiite Iran.
The overwhelming majority of the estimated two million Saudi Shiites live in Eastern Province, which neighbours Bahrain where authorities, supported by Saudi-led Gulf troops, earlier this year crushed a Shiite-led protest.
Shiites in oil-rich Saudi Arabia often complain of being marginalised.