BEIRUT — Internet service went down Thursday across Syria and international flights were canceled at the Damascus airport when a road near the facility was closed by heavy fighting in the country’s civil war.

Activists said President Bashar Assad’s regime pulled the plug on the Internet, perhaps in preparation for a major offensive. Cellphone service also went out in Damascus and parts of central Syria, they said. The government blamed rebel fighters for the outages.

With pressure building against the regime on several fronts and government forces on their heels in the battle for the northern commercial hub of Aleppo, rebels have recently begun pushing back into Damascus after largely being driven out of the capital following a July offensive. One Damascus resident reported seeing rebel forces near a suburb of the city previously deemed to be safe from fighting.

The Internet outage, confirmed by two U.S.-based companies that monitor online connectivity, is unprecedented in Syria’s 20-month-old uprising against Assad, which activists say has killed more than 40,000 people.

Regime forces suffered a string of tactical defeats in recent weeks, losing air bases and other strategic facilities. The government may be trying to blunt additional rebel offensives by
hampering communications.

U.S. State Department spokeswoman Victoria Nuland condemned what she called the regime’s “assault” on Syrians’ ability to communicate with each other and express themselves. She said the move spoke to a desperate attempt by Assad to cling to power.

Syrian authorities often cut phone and Internet service in select areas to disrupt rebel communications when regime forces are conducting major operations.

The government sent mixed signals about the Internet outage but denied it was nationwide. The pro-regime TV station Al-Ikhbariya quoted Information Minister Omran al-Zoubi as saying that “terrorists” have targeted Internet cables, interrupting service in several cities.

Separately, state-run TV said the outage was due to a technical failure that affected some provinces, adding that technicians were trying to fix it.

Activists in Syria, reached by satellite telephones unaffected by the outage, confirmed the communications problems.

A young Syrian businessman who lives in an upscale neighborhood of Damascus, which some refer to as part of “the green zone” because it has remained relatively safe, sent a text message to an Associated Press reporter Thursday that said the Internet had been cut in his area and that mobile phone service was cutting out.

The opposition said the Internet blackout was an ominous sign that the regime was preparing a major offensive.