Syria has suffered a major communications outage, which has effectively removed the country from the internet.

Syria's international internet connections were shut off at 12.26pm local time (10.26am Irish time) and remained down throughout the afternoon, US web tracking firm Renesys said.

"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 its blog.

Meanwhile, Syrian rebels battled forces loyal to President Bashar al-Assad just outside Damascus, forcing the closure of the main airport road and residents reported internet connections in the capital were down.

Residents also said mobile and land telephone lines worked only sporadically in what appeared to be the worst disruption to communications in Syria since an uprising began 20 months ago.

Syria saw last major internet outages in July and August this year, which lasted less than an hour at a time, and did not cut the country completely off from the web.