Demonstrations demanding the resignation of Hosni Mubarak, in power since 1981, have raged since Tuesday in several Egyptian cities, with the biggest clashes in Cairo and Suez. At least three people have been reported killed.
The protests, unprecedented during Mubarak's rule of a state that is a key US ally, have seen police fire rubber bullets and tear gas at demonstrators throwing rocks and petrol bombs.
A page on Facebook announcing Friday's protest gained 55,000 supporters in less than 24 hours.
"I deplore the reported deaths following the demonstrations taking place in Egypt," Ashton said in a statement.
"I call on the Egyptian authorities to fully respect and protect the rights of their citizens to manifest their political aspirations by means of peaceful demonstrations.
"I call on all parties to exercise restraint and on the Egyptian authorities to release all peaceful demonstrators who have been detained."
Mohamed ElBaradei, the former head of the UN nuclear watchdog turned Egyptian reform campaigner, said he expected big demonstrations across Egypt on Friday, and that it was time for President Hosni Mubarak to go.
ElBaradei planned to leave Vienna, where he lives, for Cairo later on Thursday to join a swelling wave of protests against Mubarak inspired by Tunisians' overthrow of their authoritarian president.
The Arabic news station Al Arabiya quoted ElBaradei, who held a number of rallies to campaign for political reform in his homeland last year, as saying he was ready to take power for a transitional period if protesters asked him to do so.
ElBaradei's arrival might provide a focus for a protest movement that so far has no figurehead, although many activists resent his long absences over past months.
In a telephone interview with Reuters, the former head of the International Atomic Energy Agency called for protests to remain peaceful, and said any use of force by the authorities would "backfire badly".
"People broke the culture of fear and, once you break the culture of fear, there is no going back," ElBaradei said.
"I think we will definitely see a change coming."
ElBaradei, who did not rule out running for president if democratic change was implemented, also made clear his view that Mubarak should not stand for president again.
"He has served the country for 30 years and it is about time for him to retire," he said. "I think he has to declare that he is not going to run again."
The next presidential election is due in September, and Mubarak, 82, has not said if he will stand again.
Suez becomes hotbed
Reuters reporters describe the port city of Suez as the most violent scene of clashes. Online activists have started calling Suez Egypt's Sidi Bouzid in a nod to the Tunisian city where protests began that toppled autocratic leader Zine al-Abidine Ben Ali 13 days ago.
Suez residents say they share many of the problems voiced by the Tunisian protesters - high unemployment, rising prices, official corruption and widespread use of torture, and have taken inspiration from Tunisia's uprising.
As in Tunisia, a large portrait of the country's leader adorns a wall on the road into town. Mubarak's face is beaming and benevolent, his arms outstretched toward his people.
"Our government is a dictatorship. A total dictatorship," said Mohamed Fahim, a 29-year-old glass factory worker, as he stood near the charred skeleton of a car that he said was burned in the protests.
Corruption and unemployment
The perception of government corruption is keen in the cities along the Suez Canal, a major source of government income.
People in Suez are well aware of the billions of dollars the canal earns for the country every year, and many complain the money does not translate into improved schools or more jobs.
Suez was caught up in three wars with Israel and people are also aware of the generous US military aid which is seen as a major support for Mubarak's government. "The youth have no jobs!" shouted a 64-year-old man.
"The companies don't have work for us!" yelled an 18-year-old girl wearing a headscarf.
One man beckoned for calm so a Reuters correspondent could write down their complaints.
"In Suez we have, today, petrol companies [...] we have factories, we have customs and we have the Suez Canal. And despite all of that, there is enormous unemployment in Suez," said 40-year-old local lawyer Kamal Hassan.
Revolution wave spreads to Yemen
In the meantime, thousands of Yemenis took to the streets of Sanaa on Thursday to demand a change of government, inspired by the unrest that has ousted Tunisia's leader and spread to Egypt this week.
Reuters witnesses estimated that around 16,000 Yemenis demonstrated in four parts of Sanaa in the largest rally since a wave of protests rocked Yemen last week, and protesters vowed to escalate the unrest unless their demands were met.
"The people want a change in president," protesters shouted, holding signs that also demanded improvements to living conditions in Yemen, the Arab world's poorest country.
President Ali Abdullah Saleh, a key ally of the United States in a war against a resurgent al-Qaeda wing based in Yemen, has ruled this Arabian Peninsula state for over 30 years.
(EurActiv with Reuters.)