Government troops were also heavily shelling the Damascus suburb of Douma, local activist Mohammed Saeed said via Skype.
Saeed and other activists bypassed the communications blackout by using satellite telephones to connect to the Internet.
In the past, the regime has cut telephone lines and cellular networks in areas where military operations are under way, but the latest blackout was the first to cover the whole country since Syrian uprising began in March 2011.
In neighboring Lebanon, tensions were running high Saturday in the northern city of Tripoli between supporters and opponents of Assad's regime, which is dominated by the president's Alawite sect, an offshoot of Shiite Islam. Lebanese troops deployed to potential flashpoints in the city — home to significant Sunni and Alawite populations and the site of deadly violence in recent months between the two communities — to prevent possible clashes.
The army dispatched troops to Tripoli as a precautionary measure after an announcement Friday that 20 Lebanese Sunnis had been killed inside Syria while fighting alongside rebels, who are predominantly Sunnis as well. The city was clam Saturday.
It was not clear when the funerals would be held because the bodies of the dead are still in Syria, Lebanese security officials said on condition of anonymity in line with regulations.
Lebanon is particularly vulnerable to getting sucked into the conflict in Syria. The countries share a complex web of political and sectarian ties and rivalries that are easily enflamed. Lebanon, a country plagued by decades of strife, has been on edge since the uprising in Syria began, and deadly clashes between pro- and anti-Assad Lebanese groups have erupted on several occasions.
In Turkey, Foreign Minister Ahmet Davutoglu said the Syrian regime has degenerated into an "armed militia" that resorts to brutality in an attempt to stay in power. Davutoglu spoke Saturday at an Istanbul meeting attended by Arab foreign ministers who expressed opposition to the Syrian government.
Davutoglu and other delegates at the one-day conference say the Syrian regime is a threat not only to its people but also to peace and security in the region.
Turkey was an ally of Syria before the crisis began but turned into one of its harshest critics because of Assad's crackdown.
AP writers Elizabeth A. Kennedy in Beirut and Peter Svensson in New York contributed to this report.