CAIRO (CNN) -- Egypt's Muslim Brotherhood canceled nationwide demonstrations Friday, except for one in Cairo's Tahrir Square against the controversial film about the Prophet Mohammed, the group said in a Twitter message.
The move comes as U.S. President Barack Obama reminded Egypt that it must take robust action against violence directed at U.S. diplomatic missions or risk a "big problem."
For the fourth straight day, tensions festered in Cairo amid widespread rage over the anti-Islam film made in the United States and posted online.
The unrest erupted outside the U.S. Embassy in Cairo as riot police clashed sporadically with protesters.
Officers armed with shields and batons, backed by an armored personnel carrier, rushed a group of several hundred protesters shortly after dawn to quell a violent demonstration that had raged through the night.
After the rush, a smaller number of demonstrators regrouped near the U.S. Embassy across from police lines, and stones and tear-gas canisters once again crossed in the air. Police fired rubber bullets at protesters. The army began constructing a wall of concrete blocks about 10 feet (3 meters) high across the road leading to the embassy.
Hours later, in the afternoon, youths climbed the newly built wall and threw rocks at police, according to eyewitnesses. Security forces fired tear gas and used water cannons to hold off the rioters.
But 100 to 200 hundred meters away in Tahrir Square, a few thousand protesters congregated peacefully.
More than 250 people have been injured and 40 arrested this week as riot police faced off with angry protesters, state media said.
Mohamed Sultan, a Health Ministry spokesman, said 15 protesters were injured from tear gas inhalation and eye irritation Friday. He said 11 protesters have been hospitalized in the past couple of days.
Nearly three dozen of those hurt were members of the nation's security forces, state media said. Among the charges for those arrested include thuggery, assaulting police officers and vandalism near the embassy.
Both the police clampdown and the cancellation of the nationwide protests come during a delicate period across the restive Middle East.
Citizens across the Middle East and North Africa have taken to the streets to protest the anti-Islam film.
The region is on edge after the killings of U.S. Ambassador to Libya Chris Stevens and three other American officials at the U.S. Consulate in the Libyan city of Benghazi.
Ties between the United States and Egypt have cooled since the overthrow last year of longtime ruler Hosni Mubarak and the election of Mohamed Morsy, the country's first democratically elected leader.
Before he became president, he had been a leader in the political arm of the Muslim Brotherhood, the popular Islamist movement.
Obama warned that relations with Egypt will be shaped by how the country responds to the violence.
"I don't think that we would consider them an ally, but we don't consider them an enemy," Obama told Telemundo in an interview that aired Thursday night.
If Egypt takes actions, Obama said, that "indicate they're not taking responsibilities, as all other countries do where we have embassies, I think that's going to be a real big problem."
Obama's comments were widely seen as a warning to Egypt, which under Mubarak was widely considered a staunch U.S. ally and remains a major recipient of American foreign aid. It is the most populous and one of the most influential nations in the Arab world.
When the protests began Tuesday, police and Egyptian troops formed defensive lines around the embassy to prevent demonstrators who had also gathered there from advancing, but not before the protesters had scaled the embassy fence and placed a black flag atop a ladder in the American compound.
Police arrested a handful of protesters at the time, but the failure of Egyptian authorities to take action sooner has been widely questioned, as has President Morsy's delayed condemnation of the attacks on American diplomatic missions.
Morsy initially focused his criticism on the anti-Muslim film as an unacceptable slap at Islam.
"The presidency condemns in the strongest terms the attempt of a group to insult the place of the Messenger, the Prophet Mohammed ... and condemns the people who have produced this radical work," the president said in a statement posted on his Facebook page. "The Egyptian people, both Muslims and Christians, refuse such insults on sanctities."
But after speaking with Obama in what the White House described as a review of the "strategic partnership between the United States and Egypt," Morsy directly criticized the attacks for the first time Thursday.
"Those who are attacking the embassies do not represent any of us," he said in comments from Brussels, Belgium, where he was visiting the headquarters of the European Union.
"I think it was a little bit of a strange choice of words to say that Egypt is not an ally," Atlantic Council analyst Michelle Dunne said. "But I think that his purpose is to put President Morsy on notice that he really has to do what's necessary to prevent the escalation of these demonstrations in Cairo to what we have seen, for example, in Libya."
On Thursday, White House spokesman Jay Carney said Obama used the correct "diplomatic and legal terms" in that the United States and Egypt do not have a formal alliance or mutual defense treaty.
But, he said, Egypt remains "a longstanding partner" of the United States, and U.S. officials have no intention of cutting aid to the country.