The United States on Wednesday criticized its ally Saudi Arabia for upholding a 20-year jail sentence on an aid worker who was accused of tweeting against the government.

"We are disappointed" by the confirmation of the sentence on Abdulrahman al-Sadhan "for peacefully exercising his right to freedom of expression," State Department spokesman Ned Price said.

"We have closely monitored his case and are concerned by allegations that Mr. al-Sadhan was subjected to mistreatment, that he has been unable to communicate with family members and that his fair trial guarantees were not respected," he said in a statement.

An employee of the Red Crescent, Sadhan was taken away from his office in Riyadh in March 2018 over an anonymous Twitter account with criticism of the ultra-conservative kingdom's rulers, according to his family.

He was first sentenced in April this year, also triggering condemnation by the United States.

His sister Areej al-Sadhan, a US citizen, wrote on Twitter on Tuesday that an appeals court confirmed the 20-year sentence followed by a 20-year travel ban.

Speaking at a vigil last week in Washington, she accused President Joe Biden's administration of enabling the verdict by not taking meaningful action against Saudi Crown Prince Mohammed bin Salman, despite finding him responsible for the murder of US-based Saudi writer Jamal Khashoggi.

She said that Saudi jailers nearly killed her brother, smashing his hand and saying, "'Is this the hand you tweet with?'"

The Biden administration has repeatedly promised to elevate human rights with the Saudis but activists criticized Biden's national security advisor, Jake Sullivan, for meeting Crown Prince Mohammed last week for talks on the war in Yemen.