US Secretary of State Mike Pompeo has urged Egypt to stop harassing US citizens.
The warning comes shortly after the release of dual US-Egypt citizen Mohamed Amashah, 24, who spent almost 500 days in an Egyptian prison.
Amashah had been held in pretrial detention for allegedly misusing social media and aiding a terror group, a punishment for holding up a sign in Tahrir Square which read: "Freedom for all the political prisoners."
Like many other political prisoners who have limited access to legal recourse, Amasha had been on hunger strike to demand his release. He eventually had to relinquish his citizenship as a condition for going home.
"We thank Egypt for securing his release and repatriation," Pompeo said at a news conference.
"But at the same time, we urge Egyptian officials to stop unwarranted harassment of US citizens and their families who remain there."
In January Mustafa Kassem became the first US citizen to die in an Egyptian prison after being detained for six years.
Pompeo had raised his case with Egypt but calls to release him were repeatedly ignored.
After he died the secretary of state expressed outrage, whilst US diplomat for the Middle East David Schenker said his death was "needless, tragic and avoidable".
Egypt is a key ally of the US, supporting its so-called 'war on terror' and the peace treaty with Israel.
President Donald Trump has called Abdel Fattah Al-Sisi his "favourite dictator".
However, over recent months the US has remonstrated with the north African country over a number of issues.
Last week a group of experts called on Pompeo to tell Egypt that military aid and other cooperation between the two countries is at stake unless the regime stops its crackdown on activists and journalists.
The issue of political prisoners remains urgent and pressing in Egypt, even more so amid the coronavirus pandemic.
There are some 60,000 political prisoners in Egypt many of whom have died due to medical neglect and poor conditions of detention.
On Tuesday, Khaled Abdel Raouf Selim died from suspected coronavirus in Banha University Hospital after being detained in Banha General Prison.