The European Union's senior diplomat returned to Cairo on Monday in a last-ditch attempt to keep Egypt from descending into civil war after the ouster of Islamist President Mohammed Morsi.
Catherine Ashton, the E.U.'s high representative for foreign affairs and security policy, was meeting with leaders of the government of interim President Adly Mansour and of the Muslim Brotherhood, the Islamist Party that came to power last year with Morsi's election.
More than 300 people have been killed in protests since the army overthrew Morsi on July 3. At least 80 Morsi supporters were killed Saturday when security forces opened fire on a Muslim Brotherhood-led march on the army's intelligence headquarters, the Health Ministry reported Monday.
In a statement, Ashton said she would try to negotiate a "fully inclusive transition process, taking in all political groups, including the Muslim Brotherhood."
But the two sides may be too deeply entrenched for Ashton to succeed. Her visit — her second in less than two weeks — came a day after the interim government further stoked fears that the violence could explode into a full war by equating Islamist supporters of Morsi with terrorists.
In remarks carried by the government's official State Information Service, Mostafa Hegazy, a top strategic affairs adviser to Mansour, said the street protests can't be "separated ... from the context of terrorism."
In comments that were seen as foreshadowing an imminent military crackdown on the protests, Hegazy said, "The state does not accept shedding blood of any Egyptian, and anyone who commits violence will be held accountable."
The Muslim Brotherhood insists it is conducting a peaceful protest and accused security forces of attacking them with live ammunition.
Gehad el-Haddad, a spokesman for the Brotherhood, said in an interview with the BBC that the only people being violent were "badly dressed thugs, police in three types of uniform and plain-clothed police."
"It may take weeks, months, more than a year — we will still hold our ground," el-Haddad said.
The government denied that its forces fired live rounds Saturday, saying they used only tear gas. It didn't explain how several dozen people died from tear gas.
The Salafist Nour Party — which swept parliamentary elections with the Muslim Brotherhood after the Arab Spring uprising in 2001 but initially accepted the interim government earlier this month — issued its strongest criticism yet on Monday, saying security forces were revisiting what it called "the 'Hitlerite' and fascist practices" of the past.
Galal al-Morra, the party's secretary general, told reporters that the new government appeared intent on "persecuting" and "marginalizing" Islamists, the Middle East News Agency reported.
"The people who have gained their freedom will not let go of it," he said.
Washington also officially registered its concern with the Egyptian government over the weekend, the White House said Monday
Secretary of State John Kerry and Defense Secretary Chuck Hagel both spoke to their counterparts in Cairo "to convey our concern about the violence and bloodshed that we saw," said Josh Earnest, the deputy White House press secretary.
"It's the view of the United States that Egyptian authorities have a moral and legal obligation to respect the right of peaceful assembly and freedom of expression," Earnest said.
Ayman Mohyeldin of NBC News contributed to this report.