DAMASCUS - Most communications were down in Syria on Thursday and clashes near the capital closed off the road to Damascus airport, monitors said, as rebels warned of a possible government assault.
A regime air strike on the northern city of Aleppo, meanwhile, killed at least 15 civilians, said the Syrian Observatory for Human Rights.
US technology companies Akamai and Renesys which monitor web traffic said the war-torn country was cut off from the Internet from 1026 GMT.
"In the global routing table, all 84 of Syria's IP address blocks have become unreachable, effectively removing the country from the Internet," said Renesys.
In Damascus, users said both Internet and mobile telephone communications were cut and land lines barely functioning, while the country's Internet provider cited technical problems.
The state news agency SANA also had its feed interrupted at midday.
According to activists, sudden communication cuts are often a signal of imminent military offensives.
Fighting between rebels and troops is currently focused around Damascus, with the army trying to dislodge rebels who have set up rear bases on the outskirts of the capital.
The fighting forced the closure of the road between Damascus and its international airport on Thursday, the Observatory said, with Dubai's carrier Emirates saying it had cancelled its flights to the Syrian capital.
"The road to Damascus international airport was closed because of ongoing fighting and military operations in the surrounding areas," the Syrian Observatory said.
Elsewhere, it said five children and two women were among at least 15 people killed when a government warplane dropped two bombs on the rebel-held Ansari district of Aleppo.
The strike hit two buildings in Aleppo, Syria's war-torn commercial capital in the north, while videos posted online by activists showed the facades of several apartments blown away.
The videos, which could not immediately be authenticated, showed residents trying to rescue a wounded child and describing how barrel bombs were used in the raid.
Also in the north, several rebel brigades attacked the fortress-like Wadi Daif army base in Idlib province and fighting raged outside the nearby insurgent-held town of Maaret al-Numan, the Britain-based Observatory said.
Rebels who control vast swathes of territory in northern Syria have made significant gains in past days, including for the first time shooting down regime's attack aircraft with surface-to-air missiles.
The Washington Post reported on Thursday that Syrian rebels have obtained up to 40 shoulder-fired anti-aircraft missiles, citing Western and Middle Eastern intelligence officials.
Some of the missiles were supplied in the past weeks by Qatar, it said.
Analysts say the use by the rebels of the advanced weaponry marked a potential turning point in their prolonged war with President Bashar al-Assad's forces, in which according to the Observatory more than 40,000 people have died since March 2011.
Since the end of July, the Syrian regime has used its aerial superiority to try to suppress the growing insurgency.
On the diplomatic front, international envoy Lakhdar Brahimi was due at 1400 GMT to brief the UN Security Council which remains divided between Western nations and Assad allies Russia and China over the Syrian crisis.
Moscow and Beijing have blocked three Security Council resolutions condemning the Syrian government.
Appointed after Kofi Annan threw in the towel, Brahimi has twice met with Assad and has held talks with a number of regional leaders in a bid to resolve the 20-month crisis.
Spain meanwhile announced its recognition of the Syrian National Coalition as the legitimate representative of Syria's people, boosting the opposition in its campaign to oust Assad.
France was the first Western state to recognise the coalition as the sole representative of the Syrian people and it was swiftly joined by Britain. Paris has also suggested arming opposition fighters.
But even as international support grew for the opposition, Human Rights Watch on Thursday accused rebels in the field of using young boys to serve as fighters, guards and lookouts in the brutal conflict.
"Children as young as 14 have served in at least three opposition brigades, transporting weapons and supplies and acting as lookouts," the New York-based watchdog said.
"Children as young as 16 have carried arms and taken combat roles against government forces."