Cairo (CNN) -- Kamal Ganzouri, who once served as prime minister under President Hosni Mubarak, regained the post Friday as competing protests drew tens of thousands of demonstrators in the capital.

"We are here to serve our nation," Ganzouri said.

Ganzouri told reporters that Hussein Tantawi, field marshal of the Supreme Council of the Armed Forces and Egypt's dominant force since Mubarak's ouster in February, "made it clear to me he is no longer willing to stay in power. If he told me otherwise, I'd not have accepted to take this role."

Ganzouri said he had asked for time to form a Cabinet "that will be accepted by everyone."

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Ganzouri took the job after Egypt's military rulers asked him to form a government of "national salvation."

The development came days after Prime Minister Essam Sharaf and his government quit en masse and days before parliamentary elections, scheduled to begin Monday. The high military council decided Friday to extend voting to two days for each stage of the election, which will take several months, according to state-run Egypt TV.

"Of course, the new government cannot be formed before Monday's parliamentary elections," Ganzouri said.

The elections will be observed by a delegation from the International Republican Institute as well as a U.S. congressional delegation "to identify and evaluate strengths and weaknesses in Egypt's election system, including campaign regulations, the balloting process, vote tabulation and reporting," the institute said Friday.

Ganzouri, who was Egypt's prime minister from 1996 to 1999, is to remain prime minister until at least January 10, when results of the parliamentary elections are finalized, said Aly Hassan, a judicial consultant. After that, Parliament would have to back Ganzouri for him to retain the position.

Russia's special representative for Africa, Mikhail Margelov, had said any new prime minister would likely play a technical role, one that will require he not only run the government but also "ensure the relevant political climate ahead of the elections," the Russian news service Interfax said.

The Alliance of the Revolutionaries of Egypt had proposed Mohamed ElBaradei, a 2005 Nobel Peace Prize winner and a frontrunner for the presidency of Egypt, to take over as prime minister, said coalition member Musad Ibrahim. He criticized the choice of Ganzouri, citing his advanced age and asserting that "all his projects (in government) were failures." Ganzouri is 78, according the Egyptian government website.

"The security council wants someone they can control, and Ganzouri is their man," Ibrahim said.

Ganzouri takes the helm at a time of tremendous change, which he acknowledged in his news conference, saying that his new responsibilities "are a lot more than I ever had ever before."

In Washington, the White House issued a statement saying that the new government "must be empowered with real authority immediately" and that the country's transition to democracy "must continue, with elections proceeding expeditiously, and all necessary measures taken to ensure security and prevent intimidation."

The Obama administration is watching the exploding tensions in Egypt with alarm, less than two months after Secretary of State Hillary Clinton praised the work of the military. But the violence against demonstrators and the resignation of the government has changed the stance of the State Department, which on Tuesday condemned the "excessive force" against protesters.

Ganzouri's appointment was not well received by some demonstrators, hundreds of whom blocked the entrance to the Cabinet headquarters in protest, according to Dr. Karim El Kholy, a dentist who had flown from Michigan to join the protests.

In Alexandria, thousands of protesters clashed with security forces around the security directorate, according to Huda El Sadi, an activist. "Protesters and a lot of thugs are currently throwing Molotov cocktails and rocks at the security forces, who are responding with tear gas and firing rubber and birdshot," he said. "Dozens have been injured."

Fourteen people were hurt in the protests, said Dr. Hisham Shiha, a spokesman for the Ministry of Health.

Demonstrations in Egypt could test whether the nation besieged by recent violent protests can remain peaceful after days of clashes.

By Friday, the death toll from the clashes during the prior six days stood at 41, including 33 in Cairo. An additional 3,250 have been wounded, Shiha said.

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He told CNN that many of the casualties had been shot by "live ammunition, rubber bullets and birdshot."

Friday's protests in Cairo's Tahrir Square have been dubbed "last chance."

Tens of thousands of people massed there Friday. Among them was ElBaradei, according to his Facebook page.

The alliance of protesters in the square "rejects the appointment of Ganzouri," a Nile TV reporter said. "They want a new name, a true national salvation government that doesn't include any old guard from the despot regime, and that the new cabinet has ministers who can represent them, their ages, their ambitions."

Demonstrators in the square have called for the interim military rulers to step down. The square was the epicenter of the movement that led to Mubarak's ouster as president nine months ago.

Also Friday, the Muslim Brotherhood was holding a "Victory to Jerusalem" demonstration, and a pro-military march started Friday afternoon in the upscale neighborhood of Abbasiya Square. There, supporters of the Supreme Council of the Armed Forces gathered in numbers smaller than those in Tahrir Square. Some held a banner that said, "To the defenders of the nation, we say Thank you." State-run Nile TV showed the crowd chanting, "The people and the military are ONE hand!" "Whoever loves Egypt doesn't destroy Egypt!" and "Enough! Enough! Let the people live!"

Meanwhile, Jehane Noujaim, an Egyptian-American documentary film producer who was arrested Wednesday, has been released, her lawyer, Ragia Omram, said Friday. And three American college students detained this week for allegedly throwing Molotov cocktails were released from police custody Friday and headed to the airport to return to the United States, an attorney and the parents of the men said.

Egypt's military leaders apologized Thursday for the deaths of protesters, vowing to prosecute offenders and pay the medical bills of the wounded.

"The Supreme Council of the Armed Forces presents its regrets and deep apologies for the deaths of martyrs among Egypt's loyal sons during the recent events in Tahrir Square," said the message, which was posted on the council's Facebook page. "The Supreme Council of the Armed Forces confirms that it is making every sincere effort to prevent such events from happening again."

CNN's Ian Lee, Ben Wedeman, Saad Abedine, Ivan Watson and Mohamed Fadel Fahmy contributed to this report.