Cairo (CNN) -- Raising his voice and sternly wagging his finger, Egyptian President Mohamed Morsy said late Sunday that he won't stand by in the wake of recent violence, declaring a limited state of emergency and suggesting more such moves could be in the offing.
"I will act, and now I am acting," the defiant Morsy said in a nationally televised speech.
Morsy -- who became the North African nation's first democratically elected president last year but since has become a target of critics accusing him of amassing power for himself and his conservative allies -- imposed a 30-day curfew in Port Said, Ismailia and Suez. Under his order, people in those governorates cannot go out between 9 p.m. to 6 a.m.
The three northeastern Egyptian cities, all of them along the Suez Canal, have been sites of deadly violence in recent days.
It began Friday when protesters angry with Morsy's regime clashed with government supporters and police in Suez, Ismailia and elsewhere.
Then on Saturday and Sunday, 38 people died and more than 630 were injured in Port Said, where a riot broke out after news broke that 21 people from Port Said had been sentenced to death for their roles in a bloody 2012 riot at the coastal city's soccer stadium.
In his Sunday night speech, Morsy claimed people in these and other places had attacked public and private institutions, "terrorized civilians," blocked roads and taken up arms.
Those "criminals" responsible will face "justice as soon as possible," the president said. He added he has instructed the Interior Ministry, which oversees security forces, "to deal properly, and also with force, against those who attack the nation's institutions."
"We will deal with them severely," he said, insisting Egyptian authorities are capable of restoring peace and security.
The president invoked the so-called January 25 Revolution, the popular uprising two years ago that led to the ouster of longtime leader Hosni Mubarak.
Many of those who hit the streets on Friday did so to rail against Morsy, a former Muslim Brotherhood leader. At one point, Morsy declared himself immune from judicial oversight and pushed through a new constitution, actions his critics say were reminiscent of Mubarak.
On Sunday, the president said some demonstrators' violent "behavior does not have anything to do with the Egyptian revolution. ... In fact, it is against the revolution."
At the same time, he acknowledged the legitimate dissent in Egypt, as well as its impact on the country, and said "dialogue is the only way to bring about stability and security."
To this end, he invited representatives from 11 political parties to a meeting Monday. His spokesman, Yasir Ali, told state-run Nile TV that this meeting "is meant to address problems in Egypt, as opposed to express anger."
It's a sentiment that Morsy himself expressed a short time earlier, saying dialogue amongst various Egyptians was the only way for the country to reach peace and prosperity.
"We are going that way, all together," he said. "God bless Egypt, and make her safe for her people and the whole world."
Troops try to restore calm in Port Said
Roads in and out of Port Said, which sits along the Mediterranean Sea at the northern entrance of the Suez Canal, were shut down Sunday as authorities tried to maintain calm after the previous day's bloodshed.
It all stemmed from a February 1, 2012, riot at the close of a match between Cairo's prestigious Al-Ahly football club and the host Al-Masry team.
That day, 73 people were killed and more than 1,000 wounded in violence between supporters of the two teams. Many died falling from bleachers inside the stadium, while others suffocated.
Two months later, Egypt's general prosecutor charged 75 people with premeditated murder and attempted murder, while three Al-Masry officials and nine police officers were charged with "assisting the murderers."
According to the prosecutor's office, those charged with assisting knew about the assault ahead of time, didn't confiscate weapons in advance, didn't stop them and -- in the case of an electricity engineer who was charged -- turned off the lights directly over the bleachers where the Al-Ahly fans were sitting right after the visiting team wrapped up its 3-1 victory.
Fans from both sides bashed each other with rocks and chairs, yet prosecutors claimed the Port Said supporters were also armed with knives and other weapons.
On Saturday, 21 of those charged were sentenced to death. That ruling subsequently spurred some of the defendant's relatives to try to storm the Port Said prison where their loved ones were being held.
In addition, the main Suez Canal administration building, provincial government buildings, banks and courts were either looted or burned by rioters, according to state media reports.
Those facilities, by Sunday, were controlled by Army units, said Gen. Ahmed Mohammed Ali, a spokesman for the Armed Forces. The troops also secured the power and water facilities in the city, he said.
Clashes for third straight day in Egyptian capital
In Egypt's capital of Cairo, meanwhile, clashes between anti-government protesters and security forces continued for a third day on Sunday.
Police and soldiers used tear gas to quell a sometimes violent demonstration near Cairo's Tahrir Square -- the symbolic center of Egypt's revolution. Demonstrators threw rocks and burned tires and boxes, according to the state-run al-Ahram newspaper.
Police closed all the main roads and highways near Tahrir Square, and vehicles were not allowed to stop or wait near the square, the state-run al-Ahram newspaper reported.
Citing the unrest in the vicinity of Tahrir Square, the U.S. Embassy closed its offices on Sunday, according to its website. The British Embassy in Cairo also closed for the day.
The National Salvation Front, one of Egypt's main opposition groups, on Sunday called for "peaceful protests" and held "the president responsible for the excessive violence used by security forces against protesters," according to a statement posted on the state-run Al-Ahram news website.
The group made several demands before it would urge people to stop protesting, including the formation of a new government and making changes to what they called the "distorted constitution" that voters passed, in a referendum, last month.
"The NSF has decided not to run in the parliamentary elections unless a comprehensive solution similar to that suggested is reached," the group said.
Journalist Ramy Francis and CNN's Reza Sayah reported from Cairo; CNN's Amir Ahmed reported Atlanta. CNN's Greg Botelho, Yasmin Amer, Chelsea J. Carter and Salma Abdelaziz contributed to this report.