BEIRUT — Explosions and heavy fighting rocked Syria’s two largest cities on Saturday, witnesses and activists said, as the Syrian government and rebel fighters struggled to gain an advantage in the country’s bloody, 17-month-old conflict.
Also, Iran’s state news agency reported that unidentified ‘‘armed groups’’ had kidnapped 48 Iranians on the road to the Damascus airport after the Iranians visited a religious shrine.
The agency quoted an official from the Iranian Embassy in Damascus as saying it knew of the pilgrims’ whereabouts and was trying to get them released, Reuters reported. It would be at least the third time since the uprising began more than a year ago that a group of Iranians had been kidnapped, apparently by rebel forces angered by Iran’s support for Syria’s president, Bashar Assad.
The latest kidnapping report could not be verified, and it was unclear who might have been responsible. But if true, the kidnapping and the greater use of heavy weapons — tanks, helicopters, and jets are involved daily now — suggest that Syria’s civil conflict is expanding and intensifying as new tactics, players, and areas are drawn into the battle for control.
Over the past week, attacks and counterattacks have been reported in at least half a dozen Syrian cities and towns, including the country’s largest Palestinian camp, in Damascus, the capital. For the first time, rebels have also used tanks they have seized, while the Syrian military has begun firing from jets in Aleppo, the country’s largest city and commercial center. Analysts have said the government’s helicopters are showing signs of wear.
On Saturday, the escalation continued.
Clashes erupted in at least three Aleppo neighborhoods, Bustan al-Qasr, Hamdanieh, and Salaheddin, according to the Syrian Observatory for Human Rights, based in Britain. Rebels in the city, contacted by telephone and via Skype, confirmed heavy fighting and said they continued to focus on seizing government buildings, with the most ferocious engagement in recent days involving a government television station.
It has been two weeks since the fighting for Aleppo started. Rebel leaders have said repeatedly that they hope to make the city a safe haven and a headquarters for their efforts throughout the country. One opposition leader in London said last week that he was already setting up a transitional government that would make ‘‘liberated’’ Aleppo its capital.
But in a conflict in which momentum swings wildly and progress is difficult to ascertain, the rebels have yet to launch a knockout blow. ‘‘It’s a guerrilla war,’’ Colonel Malik al-Kurdi, deputy commander for the Free Syrian Army, said in an interview.
So far, especially in Aleppo, that means the rebels advance and retreat, gain territory, give it up, hide among the population, and then return again for another fight. This has already occurred several times in Aleppo, and the battle over the television station offers yet another example of the current way of war in Syria.
Rebels and activists inside the city said the fighting for the complex began late Friday with a rebel assault. ‘‘My house overlooks the buildings, and I could see the clashes from my rooftop,’’ said Tammam Hazem, an activist. ‘‘Three bullets hit our house.’’
Rebels have made government buildings a priority in Aleppo. They have seized several police stations in contested neighborhoods, knocking out a base for government troops and supporters. And their initial raid on the television station, a strategic target because it is on a high hill but also symbolic and functional for any effort to set up a local rebel government, appeared to be successful.
“Our fighters got into the TV station buildings,’’ said Abu Hamza, one of the rebels in Aleppo, using a nickname that means ‘‘father of Hamza.’’ “I was there blocking the way, trying to keep out the thugs and state security guys who would try to get in.’’ But he and others said the government response was swift and typical: helicopters began firing from the air.
‘‘We couldn’t handle the chopper attacks,’’ Abu Hamza said. ‘‘We lost about seven fighters.’’ He added, ‘‘We ran out of ammunition.’’
So the rebels retreated to a nearby neighborhood, and on Saturday afternoon, Abu Hamza said they were looking for another opportunity. ‘‘Our fighters are still there, around the buildings,’’ he said. ‘‘We didn’t pull out. I went to get supplies, but I’m going back.’’
Similar scenes have been described throughout Damascus, where fighting has surged again in what some people on Twitter are describing as the ‘‘Damascus volcano Part 2.’’