Egyptians began voting on Saturday in the second round of a presidential election, pitting an Islamist against a former premier of the old regime amid political turmoil and with the post's powers still undefined.

Ahmed Shafiq, ousted president Hosni Mubarak's last prime minister, faces off against the Muslim Brotherhood's Mohammed Mursi in a two-day ballot in which 50 million Egyptians are eligible to vote.

Bedouins who kidnapped a Singapore tourist in Egypt's Sinai Peninsula Friday released him after several hours, a security source said.

"He was handed over to the security forces," the source said.

A controversial court decision on the eve of Egypt's second round presidential vote gives the nation's army the means to keep its key political role and challenge the Muslim Brotherhood, analysts say.

The constitutional court's decision on Thursday to invalidate parliament on the grounds that a third of its members were elected illegally was a blow for Islamists, who currently dominate the house but stand to lose ground in any new election.

Egypt's transition to democracy was thrown into further disarray on Friday after its top court ordered parliament dissolved and allowed a disputed candidate to remain in a divisive presidential runoff.

Activists and political figures have described the rulings as the final phase of a military coup that takes the transition back to square one.

Egypt's ruling military council said on Thursday that a presidential run-off election will go ahead as scheduled on June 16 and 17, after a court rejected a law barring one of the candidates.

"The Supreme Council of the Armed Forces has assured that the presidential run-off will take place on schedule on Saturday and Sunday," the official MENA news agency said.

The United States voiced hope Thursday that Egypt would preserve a "democratic" government after the country's top court paved the way for the military to assume parliament's powers.

State Department spokeswoman Victoria Nuland said that the United States was still studying the ruling and would not comment on it directly but voiced hope that Egyptians would enjoy the gains from last year's revolution.

Seventeen Egyptian human rights organizations said on Thursday they are challenging a justice ministry order granting army personnel the right to arrest civilians, saying it had "no basis in law."

"The decision creates extraordinary powers that have no basis in law," the groups said, describing the order as "a blatant circumvention of the official end of the state of emergency."

A senior leader of the Muslim Brotherhood's political arm in Egypt on Thursday said a court's ruling that parliament was unconstitutional was a "military coup," in a statement on his Facebook page.

A series of measures, including giving the military powers of arrests, and then the court ruling were "a complete coup through which the military council erases the most honorable period in this nation's history," said Mohammed al-Beltagi.

Egypt's top court on Thursday cleared ousted strongman Hosni Mubarak's last premier to run for president and ruled illegal the Islamist-led parliament that sought to bar him, deepening political rifts just two days before the key vote.

The decision handed legislative power back to the generals who took power when Mubarak was overthrown in a popular uprising early last year, a military source said.

Egypt's justice minister on Wednesday granted the army the right to arrest civilians, after such powers expired with the lifting of the decades-old state of emergency last month.

Adel Abdel Hamid issued a decision granting army personnel -- including military intelligence and military police -- the right to detain civilians.