Egyptian citizens living overseas have started voting on the country's new constitution, written primarily by Islamists and denounced by liberals and secularists.
Voting inside Egypt begins Saturday. The opposition has been trying to force a delay.
Many secular Egyptians fear the constitution will erode civil liberties because it boosts the role of Islamic law and does not mention women's rights.
Islamic lawmakers approved the document last month after liberal and Christian members walked out, complaining they were being ignored.
Concluding his visit to Egypt Wednesday, U.S. Assistant Secretary of State for Democracy and Human Rights Michael Posner says the United States and many Egyptians themselves are greatly concerned about what is in the constitution.
Egypt's Draft Constitution
Limits president to two four-year terms
Provides protections against arbitrary detention and torture
Islamic law, or Sharia, serves as the basis for legislation
Religious freedom is limited to Muslims, Christians and Jews
Citizens are deemed equal before the law and equal in rights
Posner says Washington believes the constitution needs to represent all Egyptians based on the universal principles of human rights. He also says many Egyptian journalists told him they are nervous about the future. He says it is critical for reporters to be able to work in Egypt without harassment.
The Egyptian army says unity talks between Islamist-backed President Mohamed Morsi and the opposition, which were to have been held Wednesday, were postponed. No new date was set.
Egypt's top general Abdel Fattah al-Sissi had tried to help resolve the country's political crisis by attempting to host the talks. The two political sides are sharply divided over the draft constitution.
Some information for this report was provided by AP, AFP and Reuters.