Human Rights Watch (HRW) has warned that 14 Shiite Muslims are at imminent risk of execution in Saudi Arabia after a supreme court upheld their death sentences in mid-July following an unfair trial over protest-related charges.

In a Thursday report, HRW cited the families of the 14 men as saying that they were transferred from Dammam to Riyadh's Ha'ir prison on July 15 without any explanation.

Some of the defendants have been kept in solitary confinement without any contact with the outside world, the report said.

The 14 Saudi citizens were among 24 defendants in a mass trial known as the Qatif 24 case. In June 2016, the Specialized Criminal Court sentenced the Shia men to death.

The defendants were convicted based on confessions they later repudiated in court. They said the confessions were made under torture.

Saudi media claim that the 24 men were members of a terrorism cell, which targeted security forces.

On August 4, the Justice Ministry defended judicial authorities' handling of the case, arguing that the sentences were reviewed and approved by 13 separate judges.

The ministry, however, did not provide any explanation about the allegations that the confessions were made under torture, and why the judges dismissed the torture reports without any investigation.

HRW warned that Saudi Arabia's execution rate has accelerated since the country's leadership change on June 21, saying the kingdom has executed 35 people during the period, compared with 39 in first half of 2017.

Saudi Arabia's public relations firms and management consultants have recently sold a reform narrative, but executions have only increased since Saudi Arabia's leadership change, and many more could be on the way, said HRW Middle East Director Sarah Leah Whitson.

Saudi Arabia carried out 153 executions across the kingdom last year. In the most stunning case of executions in 2016, Saudi Arabia executed on January 2 Sheikh Nimr al-Nimr along with 46 other people in defiance of international calls for the release of the prominent Shiite cleric and other jailed political dissidents in the kingdom.

Since 2011, Shiite majority Eastern Saudi Arabia has been the epicenter of a protest movement against discrimination by the Wahabbi dominated regime in Riyadh. The peaceful protests have been met with a brutal crackdown by the US-backed Al Saud monarchy.

Last month Amnesty International said Saudi Arabia is using the death penalty as a means to silence Shiite Muslims.