The American family of a humanitarian aid worker detained in Saudi Arabia is calling on the Biden administration to dial up the pressure on Riyadh and secure his release.

Abdulrahman al-Sadhan, 37, denied all charges against him during his appeal hearing in Saudi Arabia on Wednesday. In April, the country’s Specialized Criminal Court sentenced Sadhan to 20 years in prison, followed by a 20-year travel ban, for allegedly running an anonymous Twitter account that mocked the Saudi government.

“It was clear that he looked exhausted from the abuse,” Areej al-Sadhan said of her brother’s most recent court appearance. “He’s been isolated from the outside world and deprived of even a phone call to his family.”

Sadhan is one of scores of Saudi critics swept up in Crown Prince Mohammed bin Salman’s crackdown on dissent inside the kingdom. Forcibly disappeared in March 2018, witnesses told family members that the aid worker was tortured while held without charge in solitary confinement. Both his mother and sister are US citizens living in California, neither of whom has been allowed to speak with him.