The Qatar-based television network Al-Jazeera said its Cairo office was burned along with the equipment inside it, and called the attack an attempt by Egypt's regime or its supporters to hinder its coverage of the uprising in Egypt.
Many correspondents covering the bloody street fights in Egypt have suffered violent attacks: a Swedish journalist is recovering from being stabbed in the back, and Czech public television is withdrawing its TV crew from Egypt because of what it called "unprecedented" attacks on reporters.
"We've never seen anything like this. Not a single media outlet in Egypt today has escaped the violence," said Jean-Francois Juillard, the head of Paris-based media advocacy group Reporters Without Borders. "It's totally impossible to work as a journalist in Egypt today."
CBS News said Friday its foreign correspondent, Lara Logan, and cameramen Don Lee and Max McClellan were released after being held for a day by the Egyptian military, and are headed back to the United States. Logan had been stationed in the northern town of Alexandria.
Al-Jazeera also said a banner advertisement on its Arabic-language site was taken down for more than two hours early Friday and replaced with a slogan reading "Together for the collapse of Egypt," which linked to a page criticizing the network.
"Our website has been under relentless attack since the onset of the uprisings in Egypt," a statement from Al-Jazeera said. "While the deliberate attacks this morning were an attempt to discredit us, we will continue our impartial and comprehensive coverage of these unprecedented events."
Last week, Egyptian authorities closed Al-Jazeera's Cairo office, revoked the credentials of Al-Jazeera reporters and detained several of them for various periods.
The Committee to Protect Journalists, a New York-based media watchdog, said Thursday that it had recorded 24 detentions of journalists, 21 assaults and five cases in which equipment was taken away over a 24-hour period. Among those detained have been correspondents for The New York Times and Washington Post.
Foreign photographers reported attacks by supporters of President Hosni Mubarak near Tahrir Square in central Cairo, the focal point of increasingly violent mass demonstrations demanding the Egyptian leader step down after 30 years in power.
In Geneva, the U.N.'s high commissioner for human rights, Navi Pillay, called the detentions of journalists "clearly a blatant attempt to stifle news."
She said "one of the prime drivers of this chaos seems to have been the actions of Egypt's security and intelligence services" and called for an end to violence and an investigation into whether it was planned.
Germany summoned the Egyptian ambassador to Berlin, Ramzy Ezzeldin Ramzy, to the Foreign Ministry to protest his government's "unacceptable" use of violence against peaceful demonstrators and journalists, the ministry said.
Germany's foreign minister, Guido Westerwelle, said it was "Egyptian security forces' duty to protect peaceful demonstrators, foreign observers and journalists."
"Those who initiated those outbursts of violence, or initiate them from the background, have to be held to account, also by the judiciary," Westerwelle told reporters in Berlin, speaking alongside U.N. Secretary General Ban Ki-moon, who was visiting the German capital.
Rights groups have also been targeted.
Human Rights Watch said one of its researchers, Daniel Williams, has been missing since his detention Thursday morning by Egyptian security forces in Cairo. Another group, Amnesty International, also said two of its staff members were missing and are believed to be held by the military police following a raid Thursday on a Cairo law center.
Both organizations called for their workers' immediate release.
Meanwhile, a Swedish TV reporter covering the protests was in serious condition at a Cairo hospital after being stabbed in the back on Thursday.
Speaking a day after the attack on reporter Bert Sundstrom of public broadcaster SVT, Swedish Prime Minister Fredrik Reinfeldt urged the Egyptian authorities to "respect the journalists."
Reporters are "the eyes and the ears of the world at the moment," Reinfeldt said at a European Union summit in Brussels.
Denmark's Foreign Minister Lene Espersen said she was "appalled" by reports about repeated attacks against international journalists.
"We have seen a pattern in the past week's dramatic developments in Egypt where freedom of expression has been deliberately suppressed. We can in no way accept this," she said Friday.
Denmark's TV2 channel on Thursday aired footage of an attack on veteran reporter Rasmus Tantholdt and his cameraman, Anders Brandt. The two were on their way to the Mediterranean city of Alexandria when they were stopped at a checkpoint and then chased by an angry, club-wielding mob. They sought shelter in a shop and are now safe in an Alexandria hotel, the station said.
Both Sweden and Denmark have beefed up the travel advisories for Egypt, advising their citizens against all travel to the country. Previously, both had urged their citizens to avoid nonessential travel.
In a statement, French Foreign Minister Michele Alliot-Marie condemned "the unacceptable incidents that have compromised the security" of journalists from French media outlets, including TF1, France 2, BFM and France 24 television channels and Le Monde newspaper.
Alliot-Marie said in a separate statement Friday, she was "especially worried about the fate of three French journalists and a researcher about whom French authorities have no news."
She said she contacted her Egyptian counterpart, Ahmed Aboul Gheit, and asked him to do everything he could to ensure that the four are located and released.
Even Russia - a country consistently rated as one of the world's most dangerous for journalists - spoke out against the violence.
In a statement Friday, the Russian Foreign Ministry said "we consider the oppression of mass media representatives working within the law to be unacceptable."
On Thursday, White House spokesman Robert Gibbs denounced the "systematic targeting" of reporters covering the protests.
Two Fox News Channel journalists were severely beaten by a mob near Tahrir Square on Wednesday. Correspondent Greg Palkot and cameraman Olaf Wiig had retreated to a building, but someone threw a firebomb inside and the men were attacked as they rushed out, said Michael Clemente, Fox's senior vice president for news.
Sarah El Deeb in Cairo and Associated Press reporters around the world contributed to this report.