"I'm deeply concerned about the possibility of an escalation of tensions and the occurrence of more confrontations and demonstrations [in Egypt]," said McCain. "However, the more important question is whether the Muslim Brotherhood will adopt a moderate approach, or if some of its extremist members will be directing the constitution-drafting process and the [presidential] elections."

Members of the 100-seat constituent assembly, tasked with drafting a new national charter, were announced on Sunday. The assembly's large proportion of Islamist figures caused outrage among liberal, leftist and secular circles, which say the assembly's composition is unrepresentative of the broad spectrum of Egyptian society.

Sixty-five assembly seats are held by Islamists, 50 of whom are either members of the Muslim Brotherhood or Salafist political parties.

McCain, a Republican senator and one-time US presidential candidate, visited Egypt in February, where he met with members of both Egypt's Supreme Council of the Armed Forces (SCAF) and the Muslim Brotherhood.

Recent days have seen escalating tensions between the SCAF and the Brotherhood – featuring a heated exchange of threats and accusations – with the latter threatening to withdraw confidence from the SCAF-appointed government of Prime Minister Kamal El-Ganzouri.