CAIRO (CNN) - Outside the U.S. Embassy in Cairo, riot police sporadically clashed with protesters for a fourth straight day after a failed attempt to disperse them early Friday.
Officers armed with shields and batons, backed by an armed personnel carrier, rushed a group of several hundred protesters shortly after dawn to quell a violent demonstration that had raged through the night. Police advanced to Tahrir Square, where some officers kicked over makeshift tents.
After the rush, a smaller number of demonstrators regrouped near the U.S. embassy across from police lines, and stones and teargas 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 (three meters) high across the road leading to the embassy.
Egyptian authorities have also made 37 arrests, state news agency Egypt News reported Friday, on charges of assaulting police officers and vandalism of property near the U.S. embassy.
The heavier handed moves by authorities came after U.S. President Barack 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."
The action by Egyptian riot police came as violent protests -- sparked by outrage over an anti-Islam film made in the United States and posted online -- entered their fourth day in Cairo. The film, which denigrates the Prophet Mohammed, has sparked protests across the region.
A see-saw battle that began Thursday between protesters and the police raged through most of the night, with demonstrators throwing Molotov cocktails and rocks and authorities responding with tear gas.
Sporadic gun fire could be heard in the area around the U.S. Embassy.
At least 224 people were injured, according to Egyptian state television, Nile TV. Egypt News reported Friday that 31 police officers have sustained injuries since the protests began.
Images broadcast in the early hours of Friday showed throngs of people massed in the area, with authorities stationed in front of them, under a dark sky. Protesters were seen lighting fires and setting off fireworks, though there was no audible chanting. The clashes appeared to have tapered off before riot police rushed the protesters Friday morning.
The protests, and Obama's comments, come during a delicate period in the relationship between the United States and Egypt under Mohammed Morsy, the country's first democratically elected leader since the overthrow last year of longtime ruler Hosni Mubarak.
They also come amid heightened tensions at U.S. diplomatic missions in the Middle East and North Africa following Tuesday's attack on the U.S. Consulate in Benghazi, Libya, that left Ambassador Chris Stevens and three other American consular officials dead.
That same day, 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.
He initially focused his criticism on the 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.
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.
"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