WASHINGTON, Dec. 29 -- U.S. Defense Secretary Chuck Hagel on Sunday voiced concern about the political climate in Egypt as the Arab country braces for a constitutional referendum next month amid growing violence.

In a phone conversation with his Egyptian counterpart General Abdel-Fattah al-Sisi, the Pentagon chief discussed "the balance between security and freedom," and stressed the role of "political inclusiveness" in Egypt's ongoing transition, Pentagon spokesman John Kirby said in a readout of the talks.

Hagel "also expressed concerns about the political climate ahead of the constitutional referendum, including the continued enforcement of a restrictive demonstrations law," Kirby said.

Egypt has witnessed growing violence and a deteriorating security situation since Mohamed Morsi, the country's first elected president, was ousted by the military in early July.

The interim government in Egypt approved a new law last month regulating demonstrations in the country and mandating security forces to use rubber bullets and birdshot to disperse protesters.

The government declared the Muslim Brotherhood, to which Morsi belongs, a "terrorist group" on Wednesday, after Cairo blamed the group for a Tuesday bomb attack on the police headquarters in Mansoura city that killed at least 16 people.

The constitutional referendum has been scheduled for Jan. 14-15.