There has been strong international condemnation of the deadly crackdown against protest camps in the Egyptian capital Cairo.
US Secretary of State John Kerry said the events were “deplorable” and “a real blow to reconciliation efforts”.
EU foreign policy chief Catherine Ashton and UN Secretary-General Ban Ki-moon also deplored the use of force.
The interim government has declared a state of emergency and a curfew was in force across parts of Egypt overnight.
Protesters had been demanding the reinstatement of President Mohammed Morsi who was ousted by the military on 3 July.
The Muslim Brotherhood, which backed the protests, said more than 2,000 people died when security forces moved in to clear the two camps – in Nahda Square and near the Rabaa al-Adawiya mosque.
The interim government said 235 civilians had been killed nationwide, as well as 43 police officers. The figures cannot be independently verified.
Interim Prime Minister Hazem Beblawi defended the operation, saying the authorities had to restore security.
But Mr Kerry said it had dealt a “serious blow” to Egypt’s political reconciliation efforts.
“This is a pivotal moment for all Egyptians,” he said. “The path toward violence leads only to greater instability, economic disaster and suffering.”
The office of UN chief Ban Ki-moon said he regretted that Egyptian authorities had chosen to use force to respond to the demonstrations.
Mr Ban was “well aware that the vast majority of the Egyptian people want their country to go forward peacefully in an Egyptian-led process towards prosperity and democracy,” a statement said.
Ms Ashton “strongly condemned” the violence and called for “utmost restraint”.
“Only a concerted effort by all Egyptians and the international community might lead the country back on a path to inclusive democracy, and overcome Egypt’s challenges,” she said.
British Prime Minister David Cameron said the violence was “not going to solve anything”.
“What is required in Egypt is a genuine transition to a genuine democracy. That means compromise from all sides,” he said.
German Foreign Minister Guido Westerwelle said Wednesday’s events were a “very dangerous” escalation of violence and France demanded an “immediate end to the repression”.
Turkish Prime Minister Recep Tayyip Erdogan’s office called the violence “a serious blow to the hopes of a return to democracy”.
In a televised address, Interim PM Hazem Beblawi expressed regret for the loss of life and said the state of national emergency would be lifted as soon as possible.
The measure imposes a curfew in Cairo and several other provinces between 19:00 local time (17:00 GMT) and 06:00.
Interior Minister Mohammed Ibrahim said the police had “dealt professionally” with the protesters, and accused the pro-Morsi protesters of firing birdshot at police.
The protest sites had been infiltrated by armed gangs, he said, and ammunition had been seized from them.
Across the country, members of the Muslim Brotherhood had been arrested and were being interrogated, Mr Ibrahim said.
Following the violence, Vice-President Mohammed ElBaradei announced his resignation from the interim government.
“I cannot continue in shouldering the responsibility for decisions I do not agree with and I fear their consequences. I cannot shoulder the responsibility for a single drop of blood,” he said in a statement.
Reports said the smaller camp in Nahda Square was cleared quickly but clashes raged for several hours around the main camp near the Rabaa al-Adawiya mosque.
Egyptian TV said that by evening the security forces had seized full control of the site, and were allowing protesters there to leave.
But several Muslim Brotherhood leaders were reportedly detained, including Essam El-Erian and Mohamed El-Beltagi, whose 17-year-old daughter was reportedly killed.
A cameraman working for Sky News, Mick Deane, was also killed, as was a reporter for Gulf News, Habiba Ahmed Abd Elaziz. She was not working at the time.
Supporters of Mr Morsi – Egypt’s first freely elected president – have been staging street protests since he was ousted on 3 July.
He is currently in custody at an undisclosed location, and has been accused of the “premeditated murder of some prisoners, officers and soldiers” during a prison breakout in 2011.