DUBAI (Reuters) - Prominent United Arab Emirates (UAE) pro-democracy campaigner Ahmed Mansoor may be suffering treatment amounting to torture, including prolonged solitary confinement, U.N. human rights experts said on Tuesday.

FILE PHOTO: Ahmed Mansoor, one of the five political activists pardoned by the United Arab Emirates, speaks to Reuters in Dubai November 30, 2011. REUTERS/Nikhil Monteiro/File Photo

UAE citizen Mansoor was sentenced to 10 years imprisonment in 2018 for criticizing the government on social media.

Independent U.N. rights experts said they were “gravely concerned” for Mansoor’s physical well-being and urged UAE authorities to give him adequate medical care, ensure detention conditions meet minimum U.N. standards and either offer him a retrial or release him.

“The poor conditions of his detention in the UAE, including prolonged solitary confinement, may constitute torture,” they said in a joint U.N. statement.

Campaign organization the Gulf Center for Human Rights (GC4HR), of which Mansoor remains a board member, said this week they had heard from a source that he had ended a hunger strike he began on March 17 to protest against poor detention conditions and how his trial was conducted.

GC4HR, based outside the UAE, says his family has not been able to visit regularly to check on his health or strike status.

“Mansoor has allegedly been kept isolated in al-Sadr prison in Abu Dhabi with no bed or water in his cell and with no access to a shower. Although visits have been allowed, they are rarely offered,” the U.N. experts said.

The UAE government did not immediately respond to a request for comment.

The United Nations has previously raised concern at Mansoor’s detention. An electrical engineer and poet, Mansoor was among five activists convicted of insulting the UAE’s rulers in 2011. They were pardoned the same year.

He was arrested again in March 2017 at his home in the Emirate of Ajman, on charges of publishing false information and rumors, promoting a sectarian and hate-inciting agenda, and using social media to “harm national unity and social harmony and damage the country’s reputation”.

In May 2018, he was sentenced to 10 years in prison and handed a fine of 1 million dirhams ($270,000).

The UAE was also criticized this week by the U.N. and rights groups for the way in which Alia Abdulnoor, who died of cancer in detention on Saturday, was tried and detained.

The United Nations on Tuesday called on UAE authorities to the investigate the circumstances of 42-year-old Abdulnoor’s death and “credible allegations of torture and ill-treatment”.

The UAE denied accusations by rights groups that she was denied adequate medical care and regular contact with relatives.

Abdulnoor was sentenced in 2017 to 10 years in prison on charges including financing terrorist groups. Having previously had breast cancer, the disease recurred after her arrest in 2015. Her family denies the charges against her, saying she was raising money for Syrian families.