An entire country was effectively cut off from the internet Thursday evening, as web traffic in and out of Syria dropped to zero abruptly.

The global web monitor Akamai showed this dramatic chart of internet traffic to Syria. Times are GMT (UTC), showing Syria disappeared at 5.26pm Thailand time.

It was a drastic development more than a year into a conflict that has claimed tens of thousands of lives.

Syria was working to repair a breakdown in the main internet connection, the government was quoted as saying by state television, raising the possibility it might have been an attack by an anti-government group. The information ministry blamed terrorism.

Activists accused the government of pulling the plug on the internet, and warned the move may signal the regime is readying a major offensive on rebel fighters.

In response to the internet shutdown, Twitter users around the world began posting dial-up numbers so that people trapped in the cyber lockdown will be able to connect to the web, tech website the Next Web reports.

Cellphone service also appeared to be partially down, and there are reports that the Damascus airport had been largely shut down.

The development was almost certainly a decision by the government of President Bashar al-Assad to throw a "kill switch" - either as a precursor to some future event such as a major offensive in the country's civil war, or an attempt to halt further damaging publicity about government attacks and atrocities.

Both Egypt and Libya also threw a kill switch last year as measures against their own uprisings.

Syrian forces and rebels engaged in heavy fighting near the main airport in Damascus, the opposition Syrian Observatory for Human Rights said in an emailed statement.

Emirates and EgyptAir both cancelled flights to and from Syria.

Syria's 20-month civil war has resulted in at least 40,000 deaths, the Observatory says, and rises by about 150 a day as opposition forces seek to oust the government of President Assad.

John M. "Mike" McConnell, former U.S. Director of National Intelligence, said the Syrian opposition relies partly on the internet for its command-and-control capabilities, and that the Syrian government was effectively shutting those down.

"It's just so easy now to coordinate with mobile phones and internet platforms," and in many cases that's all that is available to the opposition, McConnell said.

By shutting off the internet, the government may hurt its own communication abilities as well, he said, but they can rely on other technologies, including older microwave technology. "They are hurting themselves to some extent but the government has other options," McConnell said.

All internet traffic in and out of Syria was shut down at 12.26pm local time (5.26pm Thailand time) without warning, according to Renesys Corp, a US-based web monitoring company.

"In the global routing table, all 84 of Syria's IP address blocks have become unreachable, effectively removing the country from the internet," Renesys said in a blog.

Akamai Technologies Inc, another US-based company that distributes content on the internet, also confirmed a complete outage for Syria.

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