US presidential hopeful
has condemned the death of an American citizen in an
prison this week, describing it as an "outrage".
, a New York taxi driver originally from Egypt who was arrested on a home visit in 2013, died on Monday. He had been on a liquid-only hunger strike since late last year and had stopped drinking fluids four days before his death.
"My thoughts and prayers are with Kassem's family at this difficult time," the former vice president said in a tweet on Wednesday. "His death, after six years in an
jail, is an outrage."
was accused of being a spy and participating in demonstrations against President Abdel Fattah al-Sisi, but denied the charges on which he was held.
In a mass
alongside more than 700 co-defendants, he was convicted of trying to overthrow the government and sentenced to 15 years in prison in 2018.
"Americans unjustly detained anywhere in the world deserve our government's full support and relentless efforts to secure their release," Biden said.
Other US lawmakers have called for
to face sanctions in the wake of Kassem's death.
Democratic Senator Patrick Leahy, who has termed the circumstances of Kassem's death a homicide, accused US President Donald Trump of abandoning an American citizen.
"The White House refused to use its leverage to obtain his release," he said according to
"Instead, Trump has called President
a 'great friend' and his 'favourite dictator'. That is as appalling, as it is insulting, to the families of President Sisi's victims."
Trump reportedly called Sisi his "favourite dictator" during last year's G7 summit.
Republican Pete King, who was Kassem's representative in Congress, called his death "an absolute disgrace".
"Egypt needs us more than we need them," he said, urging a review of US aid to Egypt and the implementation of sanctions against Sisi's government.
Both Leahy and Democratic Senator Chris Van Hollen wrote to the president on Wednesday to call for sanctions on Egyptian officials responsible for Kassem's death under the Global Magnitsky Act.
receives around $1.5 billion in aid from the US every year, making it the second largest recipient of American assistance after Israel.
There are at least six other US citizens currently detained in
, among thousands more Egyptians jailed since
seized power in a 2013 coup. According to Human Rights Watch, there are an estimated 60,000 political prisoners jailed in the country.