WASHINGTON - The US on Thursday sidestepped questions about former Egyptian president Hosni Mubarak's release, saying it was a matter for Cairo to decide, but called for his ousted successor Mohamed Morsi to be freed.

"With respect to the Mubarak trial and decisions made, this is an internal Egyptian legal matter," said State Department spokeswoman Jen Psaki.

"Our position on Mr. Morsi remains the same. We believe there should be a process for his release," Psaki said.

 Reporters had for days asked the State Department to comment on the seemingly paradoxical situation of the two leaders.

After being toppled in early 2011, Mubarak was convicted and sentenced to life in prison. That sentence was then overturned and a retrial ordered.

On Thursday, the 85-year-old Mubarak was transferred from prison to house arrest at a military hospital.

Morsi, who was democratically elected last year, was ousted by the army on July 3, and is being held at an undisclosed location. A military crackdown on Morsi's supporters has left hundreds dead.

Psaki said: "To have an inclusive process moving forward, an inclusive political process, we believe all parties need to have the opportunity to participate. It's hard to do that when there are several members of one being detained."

The United States had expressed unwavering support for Mubarak's regime during his 30 years as leader of Egypt.

After the Arab Spring of 2011, Washington accepted Morsi's election, pressuring him toward democratic and economic reform.

The US has however yet to qualify Morsi's toppling as a military coup - a move that would automatically prompt the cutting of US aid to Cairo.