(CNN) Saudi Arabia has tortured, sexually harassed and mistreated several human rights activists detained since May this year, including women, two leading international rights groups have alleged.

Activists were repeatedly tortured by electrocution and flogging, leaving some unable to walk or stand properly , with marks on their bodies and uncontrolled shaking of the hands, Amnesty International said, citing three separate testimonies.

One of the activists reportedly tried to take her own life repeatedly inside the prison, according to the testimonies, Amnesty said.

"In one reported instance, one of the activists was made to hang from the ceiling, and according to another testimony, one of the detained women was reportedly subjected to sexual harassment, by interrogators wearing face masks," the rights group said in a statement Tuesday.

In a separate but strikingly similar statement, citing "informed sources," Human Rights Watch claimed interrogators had tortured at least three of the Saudi women activists detained at the beginning of May.

The alleged torture included "administering electric shocks, whipping the women on their thighs, and forcible hugging and kissing," HRW said. After interrogations "women showed physical signs of torture, including difficulty walking, uncontrolled shaking of the hands, and red marks and scratches on their faces and necks," the sources said, according to HRW. At least one of the women attempted suicide multiple times, the rights group said.

The Saudi government rejected the allegations of torture in a statement to CNN.

"The Kingdom of Saudi Arabia's judiciary system does not condone, promote, or allow the use of torture. Anyone, whether male or female, being investigated is going through the standard judiciary process led by the public prosecution while being held for questioning, which does not in any way rely on torture either physical, sexual, or psychological," a Saudi official said.

Saudi Arabia has faced increased international scrutiny and pressure following the killing of Saudi journalist Jamal Khashoggi in the Saudi consulate in Istanbul last month. The suspects include members of Saudi Crown Prince Mohammed bin Salman's inner circle. The crown prince has denied any connection to the killing.

US President Donald Trump signaled Tuesday that he would not take strong action against Saudi Arabia or the Crown Prince over Khashoggi's death and dismemberment.

Amnesty: 'Shocking reports'

In its statement, Amnesty said several activists had been arbitrarily detained without charge since May in Dhahban Prison, in Jeddah.

HRW said it was not identifying those who had allegedly been tortured because of concerns of reprisals against them or against sources who had revealed their abuse. Amnesty said prison authorities have reportedly warned detained activists against speaking out about mistreatment.

Both rights groups called for Saudi authorities immediately to release activists who were being held solely for their peaceful efforts to advocate human rights reforms.

"Only a few weeks after the ruthless killing of Jamal Khashoggi, these shocking reports of torture, sexual harassment and other forms of ill-treatment, if verified, expose further outrageous human rights violations by the Saudi authorities," said Lynn Maalouf, Amnesty International's Middle East research director.

"Saudi authorities are directly responsible for the well-being of these women and men in detention. Not only have they deprived them of their liberty for months now, simply for peacefully expressing their views, they are also subjecting them to horrendous physical suffering."

Amnesty and HRW also urged the country's western allies to call on the Saudi government to release women's rights activists and investigate allegations of abuse in detention.

"Any brutal torture of Saudi women activists would show no limit to the Saudi authorities' campaign of wanton cruelty against critics and human rights activists," said Michael Page, HRW's deputy Middle East director.

"Any government that tortures women for demanding basic rights should face withering international criticism, not unblinking US and UK support."

UK Foreign Secretary Jeremy Hunt was last week the first British minister to visit Riyadh since Khashoggi's killing. In a statement beforehand, the Foreign Office said Hunt would call on the Saudi authorities to do more to deliver justice and accountability for the Khashoggi family.