US Secretary of State Mike Pompeo expressed outrage during a meeting with Egyptian President Abdel-Fattah el-Sisi over the death of a imprisoned American citizen.

Pompeo derided the "pointless and tragic death" of US national Moustafa Kassem following his protracted hunger strike, a US official said on Sunday.

The United States confirmed the death of Egyptian-American Kassem in a prison last week in Egypt, where he had been in custody since 2013, and promised to continue to raise concerns over Cairo's human rights record.

An Egyptian presidency statement on the el-Sisi-Pompeo meeting made no mention of Kassem's case.

Pompeo's sharp remarks signal the US government intended to place the death of Kassem, 54, high on the diplomatic agenda on the sidelines of an international peace summit in Berlin aiming to end Libya's civil war.

The death of the auto-parts dealer from Long Island, New York prompted an outcry from human rights groups, as well as accusations of medical negligence in Egypt's prisons.

The case also touched a nerve in Washington, which has cultivated close security and diplomatic ties with Egypt despite growing unease over its human rights violations under general-turned-president el-Sisi.

Activists and foreign affairs experts have called on the Trump administration to penalise its staunch Middle Eastern ally by slashing millions of dollars in security assistance. The US grants $1.2bn in annual military aid to Egypt.

Kassem was detained by Egypt in 2013 in what his lawyers described as a vast dragnet during the violent dispersal of a protester sit-in that killed hundreds of people. He was later sentenced to 15 years under a contentious anti-protest law the government often uses to silence dissent.

He maintained his innocence throughout his detention and started a hunger strike last year in protest.

El-Sisi came to power in the summer of 2013 and has overseen a sweeping crackdown on dissent, jailing thousands.