Hagel also said protection of Americans in Egypt is of the "highest priority."
But Saudi Arabia's foreign minister assured Egyptians that Arab nations will support Egypt if any international aid to the country is cut, the Saudi Press Agency reported Monday.
"The Arab and Islamic nation is rich when it comes to the support of its sons and its potentials and will not shy away from providing a helping hand to Egypt," Saud Al-Faisal said.
International response called weak, ineffective
The carnage has spurred a call from leading human rights group Amnesty International for a "full, impartial and effective investigation in the shocking loss of life."
"The interim government has already stained its human rights record -- first by breaking its promises to use nonlethal weapons to disperse pro-Morsi sit-ins and allow for the safe exit of wounded, and then by justifying their actions despite the tragic loss of lives," said Salil Shetty, secretary-general of Amnesty International, in a news release.
"The response of the international community has been weak and ineffective, even as everyone leaps to condemn the horrific loss of life. The international community must act decisively to send a message that no government can behave this way and retain any credibility."
The group documented a rise in civil strife since the July 3 coup and cited "a string of serious human rights abuses, culminating in the wholesale attack by the security forces" on pro-Morsy sit-ins last week.
"These abuses have included an alarming and unprecedented rise in sectarian violence against Coptic Christians across the country, "seemingly in retaliation for their support" for Morsy's ouster.
It cited abuses by pro-Morsy protesters "including beatings, torture and killings.
"In recent days, the scale of violence by some Morsy supporters have manifestly increased, as some attacked government buildings and police stations and personnel. Some protesters have also fired live ammunition on local residents," Amnesty said.
Mubarak in court
As the upheaval persists in Egypt, Mubarak's court cases grind on. In Cairo, a criminal court acquitted the former president in a corruption case, Egyptian state TV reported Monday.
The case stemmed from accusations of squandering public money allocated for renovating presidential palaces. He also faces at least one other outstanding corruption claim.
Separately, Mubarak is also facing a more serious accusation: that he was involved in the killing of protesters during the 2011 uprising.
A Cairo court on Saturday adjourned a retrial in that case to this coming Sunday.
Mubarak ruled Egypt, the most populous Arab country, for three decades until demonstrators opposing his rule forced his ouster in 2011. He was convicted in 2012 in the deaths of numerous protesters, but was later granted a retrial.
After a lengthy trial, he and his former interior minister, Habib al-Adly, were found guilty and sentenced to life in prison last year on charges that they were complicit in the protesters' killings. After appealing their convictions, they were granted a new trial early this year.
Mubarak has been held since his guilty verdict last year. After months spent in a military hospital, a public prosecutor sent him back to prison in April.
The ousted autocratic leader's health has been a bone of contention during his trial and incarceration. He suffered a heart attack after relinquishing power and had said that he was physically unfit to stand trial.