Syrian opposition fighters linked to the US-backed Free Syrian Army (FSA) launched a major offensive in the city of Aleppo on Friday. The main commercial center and most populous city in Syria, Aleppo has seen months of heavy fighting between the forces of Syrian President Bashar al-Assad and opposition militant groups backed by Washington and its allies in Turkey and Saudi Arabia.

Fighting in Aleppo, located close to the Syrian border with Turkey, has produced a major humanitarian crisis, with thousands of civilians killed or injured and tens of thousands forced to flee their homes. The United Nations has estimated that as many as 700,000 refugees will have fled Syria by the end of the year.

The BBC reported that members of an opposition militia, the Tawhid Brigades, led by Islamist militant Abu Kalid, a veteran of the Sunni sectarian conflict in US-occupied Iraq, claimed that a “decisive” battle for control of Aleppo had been launched.

Bashir al-Haji, a Tawhid Brigades commander, told the Guardian newspaper that some 6,000 militants were engaged in the offensive inside Aleppo. “We are not aiming to liberate the whole of Aleppo with this battle, but to regain control of most of the city,” said al-Haji.

The fighting in Aleppo is focused in and around the Jobar neighborhood, one of the limited areas of the city where FSA forces have managed to maintain a base of support and operations. However, the Tawhid Brigades appear to have only a very loose connection to the FSA, a deeply divided umbrella group headed by ex-Assad regime officers and other figures on the payroll of the CIA and the Gulf sheikdoms.

The Syrian state news agency, SANA, reported that government forces had launched a counteroffensive in Aleppo “to evict the gunmen, who have come in from neighboring countries.”

The renewed drive by opposition militias to capture Aleppo comes as the United Nations General Assembly gathers for its 2012 session in New York, where discussions have focused on the conflict in Syria and the rising tensions between the US and its Israeli allies, on one side, and the Iranian regime on the other.

There can be little doubt that the new bout of fighting in Aleppo has been sanctioned, if not planned, by Washington to further its bloody intervention in Syria even as the Obama administration sanctimoniously lectures the assembled delegates at the UN about “human rights” and “democracy.”

The Syrian opposition, augmented and led by foreign Islamist fighters, has received financing, weapons, training and intelligence from the US and its allies, while the CIA is reportedly organizing the supply lines to these “rebels” from inside Turkey.

In a sign of the growing tensions generated by Washington’s aggressive policies in the Middle East, Russian Foreign Minister Sergei Lavrov made a thinly veiled criticism of the support given to Syria’s opposition militants by the US and its regional allies in Turkey and the Gulf monarchies.

“The states that encourage the opponents of Syrian President Bashar al-Assad to give up on the ceasefire and dialogue and to demand that the regime capitulate bear responsibility for the continuing bloodshed,” said the Russian foreign minister. “Such an approach is unrealistic and encourages terrorism, which is used by the opposition.”

At the UN, the representatives of China, India, Brazil and South Africa signed a joint communiqué with Russia that affirmed their support for a negotiated settlement of the Syrian conflict. Pursuing their own interests, these countries, the so-called BRICS group of “emerging” economies, have opposed the use of military force by the US and its European allies to secure their economic and strategic interests in the Middle East, first in the NATO-led air war against Libya in 2011 and now in Syria.

The Russian government has also indicated its support for a Syrian ceasefire proposal mediated by a “quartet” of regional powers, Egypt, Turkey, Saudi Arabia and Iran. The Obama administration has so far refused to seriously acknowledge the “quartet” proposal, which was first put forward in August by Egypt’s Islamist president, Mohamed Mursi. Washington’s principal Arab ally in the Middle East, the Saudi regime, has refused to take part in negotiations over Syria that include its regional rivals in Iran.

Rather, US imperialism has used the 67th Session of the UN General Assembly as a platform to issue a series of bellicose threats against Syria and Iran. Following President Barack Obama’s belligerent speech to the assembly on Tuesday, in which he threatened war with Iran and demanded regime-change in Damascus, Secretary of State Hillary Clinton hinted that the US would consider military action against Syria that bypassed the UN Security Council.

Speaking at Thursday’s session of the Security Council, Clinton claimed that the body was in a state of “paralysis” over Syria. She then exemplified the contempt of the Obama administration toward the UN by departing the session before Lavrov spoke on the position of the Russian government.

Secretary Clinton then held a private meeting with various anti-Assad opposition groups before going on to host talks on the sidelines of the General Assembly with the so-called Friends of Syria group—a collection of European imperialist powers, Middle Eastern stooge regimes and various US assets.

The head of the Turkish-based opposition Syrian National Council (SNC), Abdulbaset Sayda, also attended this meeting. Washington and its allies have attempted to forge a closer alliance between the SNC and the disparate militias that make up the FSA, the main anti-Assad military bloc.

Largely based on reactionary Sunni Islamist militants, many of them foreign fighters with links to Al Qaeda, the armed opposition in Syria is deeply divided and has failed to win mass support inside the major urban centers of Damascus and Aleppo.

After the September 11 assault by Islamist fighters on the US consulate and a CIA base in the Libyan city of Benghazi, as well as the mass anti-American protests across the Muslim world sparked by the crude US-made Islamophobic film The Innocence of Muslims, sections of the Washington foreign policy establishment began questioning US policy in Syria and raised the dangers of “blowback” from US support for the Islamist militants now fighting the Assad regime.

The Obama administration hopes that a unified political and military opposition in Syria will be even more directly subordinate to US interests, providing Washington with a better proxy force through which it can either oust the regime in Damascus or, failing that, pressure Assad into make concessions, such as weakening the longstanding Syrian alliance with Iran.

In a statement clearly timed to maintain pressure on the Assad regime, US Defense Secretary Leon Panetta claimed Friday that the Syrian government had moved some of its chemical weapons stockpile. Panetta told a press conference at the Pentagon that there were intelligence reports of “limited” movements of chemical weapons, while the major stores remained “secured by the Syrian military.” President Obama has threatened that the use of chemical weapons by Syrian armed forces, or the inability of the regime in Damascus to secure its stockpiles, could trigger a US military intervention.