A hearing in the trial of several prominent Saudi women’s rights activists has been postponed, despite intense scrutiny of the case from the kingdom’s western partners.

The fourth hearing in the trial of 11 activists including Loujain al-Hathloul, Eman al-Nafjan and Aziza al-Yousef was cancelled at the last minute on Wednesday, a court official told some of the women’s relatives, according to Reuters. The official cited a judge who gave “private reasons” for the postponement and no new date for the hearing was set.

Foreign media and diplomats – already barred from attending previous sessions in the high-profile trial – were turned away from Riyadh’s criminal court. A panel of three judges had been expected to examine the response already submitted by the detainees to the charges against them.

It follows further arrests of the women’s family members and supporters this month, in a sign that Riyadh is not bending to international pressure over its treatment of political prisoners.

The women on trial, all active campaigners in the fight to end the country’s guardianship system that renders women second-class citizens, were arrested last May, just before Crown Prince Mohammed bin Salman lifted the longstanding ban on women driving. Among the charges they face are allegations of spying and harming Saudi interests by contacting foreign media, diplomats and human rights groups.

Since their arrest the Guardian has seen leaked medical reports saying that several of the women are suffering from malnutrition, cuts, bruises and burns, evidence which appears to contradict the authorities’ insistence that men and women in their custody are not being tortured.

Hathloul’s family have accused her interrogators of sexual abuse and torture during nearly a year in custody.

The allegations have fuelled criticism of the kingdom’s human rights record, already under intense scrutiny after the murder of the journalist Jamal Khashoggi at the Saudi consulate in Istanbul last year. While the royal family has acknowledged that a team of Saudi operatives killed the journalist inside the diplomatic mission in October, they have described the incident as a rogue operation carried out without the involvement of the crown prince.

Khashoggi’s death is believed to have led King Salman to order a review of the decision to arrest and detain about 200 men and women in a crackdown ordered by his son and heir Prince Mohammed. The medical reports viewed by the Guardian were part of recommendations made by the investigation to pardon all the prisoners or at least allow an early release for those suffering from serious health problems.

Three of the detained women – Yousef, Nafjan and the academic Dr Rokaya Mohareb – were released on bail last month. The case has also been transferred from a high-security terrorism court to a criminal court, steps taken after lobbying efforts from human rights groups and western governments.

However, at least 14 more people believed to be supportive of the women, including academics and writers, were arrested earlier in April. Among the new detainees was Yousef’s son, Salah al-Haidar. Haidar and another new detainee are dual US citizens, and one detainee is pregnant.

The Saudi government has so far not publicly commented on the latest crackdown and the new detainees’ whereabouts are unknown. Last Wednesday, the US secretary of state, Mike Pompeo, said he had pressed Saudi Arabia, a close ally of Donald Trump’s administration, to release the US citizens.

Prince Mohammed has ushered in sweeping social reforms in Saudi Arabia since he was appointed heir to the throne in 2017. Curbing the powers of the country’s notorious religious police and reintroducing cinemas and public entertainment has been accompanied by a sustained crackdown on intellectuals, businesspeople, clerics and rivals considered a threat to his power.