A special court on Wednesday sentenced 14 people to jail terms of between six months and 23 years. The sentences were second of a series over a plot to attack US forces in Qatar.

The 14 were convicted of "joining a terrorist cell that aimed to launch a terrorist attack against US forces in Qatar," the Saudi Press Agency said in a statement.

They also tried to "join a group in Syria that was coordinating the travel of young men to Iraq to join the fight there, for money," and had received military training in unspecified "Al-Qaeda camps."

The special court, established to try people charged with terror-related crimes, banned the defendants from traveling after serving their jail sentences, for periods equal to their duration of imprisonment.

It said the 14 represented the second group of 41 defendants who belonged to the same cell.

On Tuesday, the Riyadh-based court sentenced 13 people to between 18 months and 30 years. They included an Afghan, a Qatari and 11 Saudis.

The first group was also found guilty of plotting to attack US forces in Kuwait, SPA said, without giving dates. Authorities in 2011 established special tribunals to try Saudis and foreigners accused of belonging to Al-Qaeda or of involvement in deadly attacks in the kingdom from 2003-2006.

The latest convictions come with Qatar and Saudi Arabia participating in US-led airstrikes against Islamic State extremists in Syria.

American warplanes have also bombed IS in Iraq.

Separately, the criminal court in Riyadh on Tuesday sentenced two people to death for rioting, damaging public property, and calling for the overthrow of the government, in protests that took place in Al-Awamiyah governorate in Al-Qatif.

In its preliminary rulings, the court also sentenced a third person to 12 years in prison for participating in the protest actions and violence. He was also banned from traveling for 12 years after his release.

The court found the two people guilty of participating in marches calling for the toppling of the government, planning to kill security officers, and throwing petrol bombs at the Al-Awamiya police station.

The court ruled that they had participated with criminals in breaking into a pharmacy in Al-Awamiya, damaging its contents, stealing medicine and bandages to treat injured fellow protestors, and harboring those who shot at police officers during the riots in Al-Qatif.

They were also guilty of harboring a people who exploded a gas cylinder next to Al-Awamiya police station, in addition to other charges.

The defendants have 30 days to appeal the ruling.

Meanwhile, the special court in Riyadh jailed four women from four to 10 years for adoption of deviant ideas, support of Al-Qaeda, encouraging their sons to travel to conflict zones for fighting there and providing financial support to terrorist groups.