Syria’s civil war went off­line Thursday as millions of people tracking the conflict over YouTube, Facebook and other high-tech services found themselves struggling against an unnerving national shutdown of the Internet.

The communications shutdown immediately evoked memories of similar action by Libya’s Moammar Gaddafi and Egypt’s Hosni Mubarak, and it sparked fears that President Bashar al-Assad could be preparing to take even harsher action against Syrian opposition forces, which have recently made significant advances in the battle against the government.

A Syrian official blamed the outages on technical problems. Analysts said it was far more likely that Assad had ordered the Internet and some cellphone connections switched off, although it was possible that a rebel attack had severed crucial cables.

Whatever the cause of the blackout, it was clear that the remarkable window into the war offered by technology had dramatically narrowed for Syrians on both sides of the conflict and the many outsiders following the story. Observers said it signaled the beginning of a dangerous new phase after 20 months of escalating conflict.

“In some ways, it’s a Cyclops stabbing itself in the eye,” said Joshua M. Landis, a Syria expert at the University of Oklahoma. “They’re turning the light out on themselves here, which is not good.”

Post reporter Craig Timberg sits down with us to discuss the Syrian Internet blackout, whether the rebels are behind it and how it may impact the continuing conflict. (The Fold/The Washington Post)

The shutdown came amid scattered rebel gains Thursday and intensified fighting that shut down the Damascus airport. In Washington, meanwhile, officials indicated that the Obama administration was moving toward recognizing a newly formed opposition coalition as the legitimate representative of the Syrian people.

‘There will be panic’

The rising popularity of smartphones and the Syrian government’s sharp limits on the movements of independent journalists have made social media an especially vital source of information about the conflict. The abrupt loss of the technology has caused widespread fear, said Ammar Abdulhamid, a fellow at the Foundation for Defense of Democracies.

“Not everyone will have access” to news about the conflict, said Abdulhamid, who has close ties to Syria’s opposition. “There will be panic. There will be fear.”

Syrian rebel forces have many satellite phones. But the devices expose users to risk of detection by government forces, and there are not enough of the phones to keep millions of Syrians informed.

“Most of the activists, especially in Damascus, are relying totally on the local Internet services, which are delivered by the Syrian communication companies,” said Ahmed Radoun, an activist in Hama who works for an opposition news service. “They want to pressure the activists who rely on the Internet services from the local companies and to limit the news delivery to the TV channels and the news agencies we deal with.”

The government has shut down Internet services previously, as well, often in specific regions right before launching attacks. On at least two other occasions, the outages were national in scope.

Omar Abu Laila, a spokesman for the rebel fighters in the eastern city of Deir al-Zour, said communications have been down for so long there that the new disruptions will have no impact. “The communication outage did not affect us,” he said. “You should report that we’re happy the rest of Syria joined us.”

How can an entire country be taken offline?

Yet, Thursday’s blackout — at 12:26 p.m. Damascus time, according to the Internet monitoring company Renesys — set off alarms worldwide. Among the worries: The only Syrian networks still routing traffic into the nation have a history of delivering malware to opposition activists, meaning that they almost certainly are controlled by the government.

Window into the conflict

The Syrian civil war has played out with unnerving intimacy for viewers of YouTube. Shaky videos delivered images of dead children, the bloodied walls after a massacre and, just this week, the fiery streak of an opposition missile destroying a government helicopter.

Analysts said the image of that attack, which highlighted the opposition’s rising military capabilities, may have prompted Assad to cut off communications after months of allowing information to flow with relative freedom.

The government had reason to do so. Its forces used the Internet for some routine communications. Easy access to the Web also helped the government spy on opposition forces, which relied on such technology to communicate. Social media sites, meanwhile, were popular with civilians, and continued access to the sites lent a veneer of normalcy in Damascus, the capital.

Yet most blamed Assad for the Internet shutdown. The main telecommunications cables are controlled by the government-owned Syrian Telecommunications Establishment, and all of the country’s Internet providers and cellphone companies rely on the data it provides. Shutting down the flow of information, analysts say, is easy.

“It’s a sign that the regime is going to take its gloves off,” said Andrew J. Tabler, a senior fellow and Syria expert at the Washington Institute for Near East Policy. “They’re going to make sure they’re the only ones who can communicate, or at least they are going to try.”

Opposition forces, however, have grown savvy at distributing images from the fighting to keep their cause visible to the world. Rebels operating near international borders, such as with Jordan, Turkey or Lebanon, have access to cellphone signals emanating from those countries. Governments backing the Syrian opposition have sent thousands of satellite phones to the rebels; the U.S. State Department says it has sent 2,000 pieces of communications equipment, which could assist in distributing videos even if the Internet remains shut down.

“Syria is going to be an excellent test” of such initiatives, said Andrew McLaughlin, a former top policy official at Google who also worked as a White House technology adviser. “People have been preparing for this day. . . . I’ll be glued to my screen for the next 24 to 48 hours to see if that did any good.”

Dehghanpisheh reported from Beirut. Ahmed Ramadan in Beirut also contributed reporting.