Egypt's interim cabinet has chosen lawyer and social democrat Ziad Bahaa El-Din as new deputy prime minister, prime minister designate Hazem El-Beblawi said on Friday.

Bahaa El-Din, a founding member of the Egyptian Social Democratic Party, said early Friday on his Facebook page that he had accepted the posting.

He went on to say that he had been informed of the offer earlier this week but had hesitated to accept it due to Egypt's current state of "acute polarisation."

"There is a risk of failure and legitimate concerns that we are heading to a new authoritarianism... and further violence," he said.

"But such concerns are only warranted if we give in to fear and lose hope in our ability to change such a fearful course," Bahaa El-Din asserted.

He added: "I hope that I have made a wise decision and that the country finds its way to consensus, justice and development."

Bahaa El-Din, along with reform campaigner Mohamed ElBaradei, was intitially nominated for Egypt's premiership.

But Egypt's Nour Party – the second largest Islamist party after the Muslim Brotherhood's Freedom and Justice Party – opposed both choices, further stalling the troubled transition process.

ElBaradei was subsequently appointed Egypt's vice-president.

Liberal economist Hazem El-Beblawi was appointed on Tuesday by interim President Adly Mansour to top the new administration, following the overthrow of elected president Mohamed Morsi last week by Egypt's armed forces amid mass demonstrations calling for his removal.