US President Barack Obama has called for Egyptian authorities to release political activist Ahmed Maher.

Speaking at the Clinton Global Initiative in New York, Obama addressed civil society freedoms and the heavy restrictions they face worldwide.

"We stand in solidarity with those who are detained at this very moment … in Egypt, Ahmed Maher … And so many others. They deserve to be free. They ought to be released," Obama said.

"It is precisely because citizens and civil society can be so powerful – their ability to harness technology and connect and mobilise at this moment so unprecedented – that more and more governments are doing everything in their power to silence them," he added.

"From Hungary to Egypt, endless regulations and overt intimidation increasingly target civil society," Obama also said, "This growing crackdown on civil society is a campaign to undermine the very idea of democracy."

Maher, the ex-head of April 6 Youth Movement, is serving a three-year jail term, along with two other prominent activists, Ahmed Douma and Mohamed Adel, on charges of holding unauthorised demonstrations and using force against the police.

He has been on hunger strike since 15 September, along side at least 80 others prisoners, against the protest law, which was issued last November. The controversial law has led to the arrest of hundreds of people at peaceful protests.

A Cairo court banned all activities of the April 6 Youth Movement, ruling on a lawsuit that accused the group of espionage and defaming the Egyptian state.

The group, which played an important role in the January 2011 uprising that toppled Hosni Mubarak, was subject to a campaign of defamation that accused its members of being agents of foreign countries, paid to stir instability in the country.