Fighting between Syrian government forces and the US-backed opposition escalated over the weekend, with press reports of the most intense combat in the capital city, Damascus, since the campaign against the regime of President Bashar al-Assad began 15 months ago.

In Damascus, the BBC reported that anti-Assad gunmen opened fire on a power station and a bus carrying Russian oilfield workers. Government forces responded by bombarding the northern district of Qaboun and entering it in armored vehicles, raiding houses and exchanging fire with elements of the Free Syrian Army (FSA), the principal US-backed armed group.

The Associated Press reported that FSA gunmen appeared Friday in Kfar Souseh, a suburb of Damascus, marching openly in an opposition rally, their first armed demonstration in the capital city.

Fighting was also reported in the Damascus neighborhoods of Barzeh and Mezze, and some witnesses cited in the Western press—albeit anonymously—said that army tanks had opened fire for the first time inside the capital city. A BBC correspondent who later visited one of these neighborhoods found no evidence of tank fire, however.

There were also reports Sunday of heavy shelling of villages near Homs, the country’s fourth-largest city, and in the town of Deraa in southern Syria, where the first protest demonstrations against Assad took place in March 2011. Opposition groups outside Syria gave unconfirmed casualty totals of 38 dead in Homs and 17 in Deraa.

While the opposition spokesmen continue to portray the violence as a one-sided slaughter by the forces loyal to the Assad regime, there are mounting press reports of an escalating military conflict throughout the central part of the country—the entire region between Damascus and Aleppo.

McClatchy News Service reported: “The rebels now control a widening swath of territory in north and central Syria. They use it as a base for storing and manufacturing weapons and for launching attacks against government soldiers in what previously had been relatively peaceful parts of the country. In May, at least 404 government soldiers and police officers lost their lives in combat with the rebels, according to burial notices published by the Syrian government news agency, SANA…”

FSA commanders showed new weapons received through supply lines from Saudi Arabia, and boasted of an influx of cash as well. The Washington Post reported that the FSA has begun paying cash stipends to local fighters of between $50 and $100 a month.

The Post noted Saturday that the FSA is “stepping up its attacks on government troops while the world’s attention has been focused on pressuring Syrian President Bashar al-Assad to comply with a UN cease-fire and halting the massacres of civilians. The loosely organized Free Syrian Army now acknowledges that it is also no longer observing the truce…”

The Post noted that the Obama administration has approved efforts by Gulf states such as Saudi Arabia and Qatar to funnel weapons and cash to the FSA. It also reported two new fronts in the internal civil war, in the area between Aleppo and the northern border of Syria with Turkey, and in the western region around the port city of Latakia.

The state-run news agency SANA confirmed heavy fighting in the town of Haffa, between Latakia and the FSA-held area around Idlib, and reported that “terrorist groups” in Haffa had committed “heinous” crimes, including setting fire to the national hospital in the town.

There were numerous warnings on the weekend that Syria was on the brink of a sectarian civil war, in which adherence to one or another sectarian or ethnic group—Alawite, Sunni, Christian, Druse, Kurd—could become the basis of bloody violence.

British Foreign Secretary William Hague, commenting on the series of reported massacres in Syria, suggested that the country was beginning to resemble Bosnia in the 1990s. “Neighboring villages are attacking and killing each other,” he said. “We are on the edge of that kind of sectarian murder of a large scale.”

While Hague’s comments were aimed at mobilizing public opinion behind a “humanitarian” intervention in Syria, the comparison to Bosnia actually contradicts the claims that the Assad regime itself perpetrated the slaughters at Houla and Qubeir, suggesting instead that irregular forces drawn from villages populated by the minority Alawite sect may have been responsible.

UN special envoy Kofi Annan has also warned that Syria was facing an outbreak of sectarian violence between the minority Alawite sect, an offshoot of Shiite Islam to which the Assad family belongs, and the Sunni Muslim majority.

The Washington Post reported that sectarian retaliation was likely, quoting one FSA gunman who declared, “There are some Alawite towns that have taken part in the violence, and we will take revenge.”

The main responsibility for the outbreak of sectarian violence lies with the imperialist powers that have sought to manipulate the complex sectarian and ethnic divisions of Syria and other countries in the region for their own reactionary ends. In the same way, the Bush administration ignited a bloodbath between Shiite and Sunni gunmen in Iraq in 2006-2007 as a means of diverting and suppressing opposition to the US occupation regime.

The Obama administration is stepping up pressure on Russia to accede to the US-led campaign for an escalation of sanctions and outright military intervention to overthrow the Assad regime. State Department envoy Fred Hof visited Moscow Friday for talks with Russian officials, with little result, according to press reports.

After the Hof mission, Foreign Minister Sergei Lavrov said Russia will continue to oppose any resolution by the UN Security Council to sanction military intervention in Syria. Referring to Britain, France and the United States, he said that outside powers were encouraging the armed opposition in Syria to hope that “the Libyan scenario” would be repeated.

Within the United States, the campaign against Syria has increasingly taken on an overtly anti-Russian character. In a speech on the Senate floor Thursday, Senator John McCain, the leading Republican Party advocate of military intervention, complained, “US policy in Syria now seems to be subject to the approval of Russian leaders who are arming Assad’s forces.”

The Washington Post published an editorial Saturday condemning “illusions that the bloodshed in Syria could be stopped by United Nations diplomats” and declaring that no support could be expected from Russia to “install a political model in Damascus that Vladimir Putin is fighting to prevent in Moscow.” The editorial all but demanded military action, concluding “the transition in Syria will begin only when Mr. Assad is confronted with irresistible force.”

The New York Times published a similar editorial the same day, headlined “Assad, the Butcher”—a label that the Times has never applied to American presidents, including both George W. Bush and Barack Obama, whose killings as commander-in-chief dwarf those of the Syrian ruler.

Having played a key role in promoting the lies about Iraqi weapons of mass destruction and championing the bloody intervention for regime-change in Libya, the Times wrote sanctimoniously, “By enabling the Syrian dictator, Russia and China also have blood on their hands.”

The editorial called for indicting Assad for crimes against humanity and imposing a full arms embargo. It declared the diplomatic effort of Kofi Annan to be a failure, saying, “All it has done is give Russia, China and some other members of the United Nations Security Council six more weeks to excuse their inaction.”