BEIRUT, Lebanon — A Saudi teenager who faced possible execution for acts he was accused of committing as a child has been handed a 12-year prison sentence instead, a human rights group that has been monitoring his case said on Sunday.

Last year the Saudi public prosecutor’s office sought a death sentence for Murtaja Qureiris, now 18, but the threat of execution did not become public until last week, drawing international condemnation. The charges filed against the teenager related to his attendance at antigovernment protests, some that took place when he was as young as 10. The charges included possessing a firearm and joining a terrorist organization.

He was arrested at 13 and has been held in prison since.

The judge overseeing his case delivered the sentence on Thursday, according to the rights group, the European Saudi Organization for Human Rights, which has tracked the case for years.

According to the group, the judge told the teenager’s lawyer that instead of the death penalty, he would receive a 12-year sentence that would include the four years he has already served and four years of probation after his release, meaning he would serve three more years in prison.

It is unclear what led to the decision, but rights groups attributed it to international pressure over his case.

“This is a political decision after international media talked about this case,” said Ali Adubisi, the director of the European Saudi Organization for Human Rights.

But Mr. Adubisi said another court hearing was set for this week, during which prosecutors might argue for a harsher sentence, and the defense lawyer for a lighter one.

CNN first reported the change in Mr. Qureiris’s sentence on Sunday.

Executions are common in Saudi Arabia, which has been accused of targeting the kingdom’s perceived political opponents and members of the minority Shiite population through the courts. Still, it is unusual for the authorities there to execute someone accused of acts committed at such a young age.

Saudi Arabia has firmly defended its use of the death penalty. The predominantly Sunni kingdom has put 37 men to death this year, most of them Shiites, for “terrorist” activity and causing “sectarian discord,” the official Saudi news agency reported.

Mr. Qureiris was 10 when he helped lead a group of children in a demonstration against the Saudi authorities in the eastern part of the country in 2011, a time when Arab Spring protests were causing upheaval around much of the Middle East. The Saudi government harshly curbed similar protests in the kingdom’s eastern, largely Shiite provinces, with violence and mass arrests.

He was arrested three years later, in September 2014, and held for nearly four years before his first court hearing last August, the Saudi rights group said. He was initially held in solitary confinement and deprived of access to a lawyer, according to the group.

At least three other young men — Ali al-Nimr, Dawood al-Marhoon and Abdulla al-Zaher — stand accused of committing crimes as minors and have been sentenced to death, according to the United Nations High Commissioner for Human Rights.