CAIRO, July 12 (Reuters) - Egypt's interim authorities have nominated lawyer Ziad Bahaa El-Din, who is a member of the leftist Egyptian Social Democratic Party, as deputy prime minister, Prime Minister Hazem el-Beblawi said on Friday.

"I have chosen Dr. Bahaa El-Din as deputy prime minister and sent the nomination to the president," Beblawi said, adding he was holding talks with other candidates for his new cabinet that he expects to be formed within a few days.

Economist Beblawi was named prime minister to lead an army-backed government following the military's overthrow of elected Islamist President Mohamed Mursi on July 3. (Reporting and writing by Yasmine Saleh; editing by Mike Collett-White)