(CNN) -- Despite claims to the contrary, the Syrian government is almost certainly responsible for a blackout Thursday that shut down virtually all Internet service in the country, according to a leading Web security firm.
"The Syrian Minister of Information is being reported as saying that the government did not disable the Internet, but instead the outage was caused by a cable being cut," writes Matthew Prince, CEO of CloudFlare. "From our investigation, that appears unlikely to be the case."
Fighting again between rebels and forces loyal to President Bashar al-Assad disrupted much of Damascus on Friday, and there was no Internet service throughout much of Syria for a second straight day. The airport was closed to flights, and fighting killed another 31 people across the country on Friday, according to an opposition group that counts casualties.
A Syrian government information minister said that "terrorists" -- which is how the Assad regime refers to rebels in a bloody, ongoing civil war -- cut the cable, knocking out Web communication with other countries.
Rebels have routinely used the Web to transmit images of the civil war, including what they claim have been military attacks by the Assad regime on civilians.
But Prince said only four Internet cables connect Syria to the outside world. Three of them run underseas, and the fourth is an overland line through Turkey.
"In order for a whole country outage, all four of these cables would have had to been cut simultaneously," he wrote. "That is unlikely to have happened."
Connections in all regions of Syria, not just routes in some, were shut down in the outage, which began at 5:26 a.m. EST on Thursday, he wrote. The exclusive provider of Web service in Syria is the state-run Syrian Telecommunications Establishment.
The last four sites accessed on CloudFlare before the outage were a photo-sharing site, a Syrian news site, a Muslim-oriented social networking site and a porn site, according to Prince.
"In other words, traffic from Syrians accessing the Internet in the moments before they were cut off from the rest of the world looks remarkably similar to traffic from any part of the world," he wrote.
Web analytics company Renesys, which has closely monitored the Syria situation, reported Friday that a small handful of "net blocks" that had survived the original blackout had been yanked offline, as well.
Renesys originally reported that about 90% of Syria's Internet connections were offline. A graphic on the firm's site Friday showed virtually no service remaining.
Syrian government sites, however, had remained accessible because they're hosted in other countries, including the United States. The New York Times reports that several hosting companies said they were working late Thursday to take those sites down.
The U.S. government has been providing Syrian rebels with "non-lethal equipment," including communication tools to get around Internet outages.
"The Syrian government has been monitoring (the Internet) for years. They have been using the Internet with Iranian assistance to track opposition activists, arrest and kill them," said Robert Ford, the U.S. ambassador to Syria, in Washington on Wednesday.
Meanwhile, Web giant Google is pitching in, enabling in Syria a service that lets users post messages to Twitter by speaking into a mobile phone. The service, Speak2Tweet, was developed by Google and Twitter about two years ago when Web access was shut down during a civil movement in Egypt.
"In the last day, Internet access has been completely cut off in Syria. Unfortunately we are hearing reports that mobile phones and landlines aren't working properly either," the company wrote in a post on its Google+ site. "But those who might be lucky enough to have a voice connection can still use Speak2Tweet by simply leaving a voicemail" on one of several devoted phone lines.
Doug Gross, CNN