The Muslim Brotherhood has called on supporters to take to the streets, raising fears of more violence in Egypt.
The call by the group for a "Friday of Anger" came as the authorities raised the death toll from clashes this week to more than 620, mostly civilians.
On the diplomatic front, the United Nations Security Council has urged Egyptians to exercise “maximum restraint” and embrace "national reconciliation" following the military's ouster last month of Islamist-backed President Muhammad Morsi.
The statement was released after an emergency Security Council meeting on August 15.
Egypt’s interim presidency, meanwhile, has released a statement rejecting international criticism of the security forces' crackdown on the Islamists, including from U.S. President Barack Obama.
The statement said the criticism was not based on "facts" and could encourage activities by "violent armed groups."
In his remarks on August 15, Obama said normal U.S. cooperation with Egypt could not continue in the wake of the violence. He announced the cancelation of the Bright Star military exercises planned to be held with Egypt, and said further measures were being considered.
"We have sustained our commitment to Egypt and its people but while we want to sustain our relationship with Egypt our traditional cooperation cannot continue as usual when civilians are being killed in the streets and rights are being rolled back. As a result, this morning we notified the Egyptian government that we are canceling our biannual joint military exercise, which was scheduled for next month," Obama said.
"Going forward, I have asked my national security team to assess the implications of the actions taken by the interim government and further steps that we may take as necessary with the respect to the U.S.-Egyptian relationship."
At the U.S. State Department, spokeswoman Jen Psaki issued a call for an end to the violence.
"The United States strongly condemns all attacks and acts of violence and bloodshed across Egypt. We are outraged and deplore in the strongest terms the reprehensible attacks of the past few days against numerous Coptic churches," she said.
"We also condemn the recent attacks on public buildings, including police stations. There can be absolutely no place for such violence in Egypt, and we call on all of Egypt's leaders to condemn such attacks."
The United States, which provides $1.5 billion annually in mostly military aid to Egypt, said it was canceling joint exercises with Egypt’s military. Washington has called for U.S. citizens to leave the country.
The office of interim President Adli Mansour said the country was facing what it called "terrorist acts targeting government buildings and vital installations."
Violence reported on August 15 included attacks on security forces, the burning of government offices in Giza, and attacks on Christian churches across the country.
Regional power Turkey, which has voiced strong criticism of the military crackdown, said it was recalling its ambassador from Cairo for consultations. Egypt responded by recalling its ambassador from Turkey.
Ahead of the UN meeting, Turkish Prime Minister Recep Tayyip Erdogan had accused the West of ignoring the Egyptian bloodshed.
Reports quoting officials said at least 623 people died and thousands were wounded after police cleared two Muslim Brotherhood camps in Cairo set up to protest the July 3 military overthrow of the democratically elected Morsi.
Morsi’s overthrow came after millions of Egyptians took to the streets to demonstrate against the president's links to Islamists and his government’s failure to reverse Egypt’s economic decline since the 2011 revolution.
The military says it removed the president -- who remains in detention -- in response to public sentiment.
With reporting by Reuters, AP, and AFP