CAIRO - Syrians were unable to connect to the Internet for the second day on Friday, as flights in and out of the country's main international airport were cancelled as fighting raged around it. Phone lines in Syria were also disrupted.

"In the global routing table, all 84 of Syria's IP address blocks have become unreachable, effectively removing the country from the Internet," American networking company Renesys wrote on its blog after Thursday's blackout.

Graphs illustrating Syria's internet usage showed it plummeting to zero at 12:26pm local time, and it hasn't come back since.

Syria's information minister blamed "terrorists" - its catch-all word for rebel fighters - while the opposition accused the regime of President Bashar al-Assad of being behind the blackout. There have previously been blackouts in certain towns and areas, but never in the whole country.

"It is not true that the state cut the Internet," Information Minister Omran al-Zoabi told state television. "The terrorists targeted the Internet lines, resulting in some regions being cut off."

But doubt has been cast on that explanation by networking experts.

"Syria has 4 physical cables that connect it to the rest of the Internet," wrote Matthew Prince, CEO of CloudFlare, in a blog on tech site Gizmodo. "Three are undersea cables that land in the city of Tartous, Syria. The fourth is an over-land cable through Turkey. In order for a whole-country outage, all four of these cables would have had to been cut simultaneously. That is unlikely to have happened."

"The systematic way in which [network] routes were withdrawn suggests that this was done through updates in [regime] router configurations," he added, "not through a physical failure or cable cut."

Meanwhile, fighting around the Damascus International Airport grounded all flights Thursday into Friday and prevented any from coming in.

The airport road was reportedly re-opened on Friday afternoon and the head of Syria's Civil Aviation Authority said the airport was operating "as usual," according to the Associated Press.

But State Department spokesperson Victoria Nuland told reporters that "fierce fighting" had kept the airport closed on Friday. An official from Royal Jordanian, national airline of neighboring Jordan, also told ABC News that no flights were going in or out of Damascus, and flight tracking website Flightradar24.com showed no planes over Syrian airspace on Friday night.