Free Syrian Army fighters
Free Syrian Army fighters in the Handarat area near Aleppo Central prison, July 7, 2014. Reuters/Hosam Kata

Soldiers with the Islamic State of Iraq and Syria (ISIS) clashed with rival opposition groups and the Syrian military Tuesday in the town of Akhtarin -- foreshadowing what opposition fighters in the northwestern part of the country said was an imminent battle for Aleppo, Syria’s largest city.

Nearly two years ago, men living in the suburbs of Aleppo were preparing to head to Salaheddin, the main district in the city, to fight President Bashar Assad’s forces. More than a year had passed since the revolution began and the military was still in control of perhaps the most important stronghold in the entire country. But on July 19, 2012, opposition soldiers made a bold move to seize the city, giving them access to the hub of the country’s economic activity. Now the battle for Aleppo has reignited and those same soldiers who first invaded the city in 2012 said they expect the fight to be even more brutal this time.

The fall of Aleppo would be disastrous to the opposition, which has held the city for two years. The city is the largest in the country and is the main trade center. It is a strategic stronghold for the opposition, even more so than Homs, which the Syrian military seized in April. Homs had long been called the “heart of the revolution,” but never held as much tactical promise as Aleppo.

“If Aleppo fell, we could say bye-bye to Syria,” Barry Adbul Lattif, a Syrian activist from Al Bab who used to fight under the umbrella of the Free Syrian Army (FSA) before ISIS took over the town two months ago, said. “Syria will split into two parts, one piece for Assad and one piece for ISIS, and there will be no room for the activists or the FSA.”

For slightly more than 10 days, the Syrian military has conducted airstrikes on the town of Azaz, 20 miles northwest of Aleppo, in an attempt to eliminate opposition offensives around the city.

“Assad’s jets are bombarding the northern cities around Aleppo every day," Lattif said. "They are trying seriously to take siege around the liberated areas of Aleppo.” Lattif said Syrian military jets bombed Azaz yesterday, killing five people.

According to the Facebook page of the British Observatory for Human Rights -- one of the only monitoring groups in the country -- Syrian military planes attacked the town of Marea and carried out a raid in Tal Rifaat. The attacks damaged several houses and killed one, according to the organization.

Although the situation in the areas around Aleppo looks similar to that of July 2012, opposition soldiers said the battle for the city will be different this time.

Members of the former Al Bakr battalion in Al Bab were some of the original fighters to enter Aleppo in 2012 to take on the military. Lattif was one of them. They were forced to leave Al Bab, their home and safe haven after ISIS took it over more than 5 months ago. Almost all of them have abandoned the fight and fled to places such as Azaz and Kilis, Turkey.

The increasing presence of extremist forces in Syria in the past two years has changed the battle ground dynamic. Now battalions under the FSA that struggled to stay alive under Assad’s bombardment are having to fight off ISIS, too.

For the past two years, various opposition groups occupied districts in the city, including battalions affiliated with the FSA and those fighting under the direction of Salafists -- a distinct sect of Sunni Islam. ISIS repeatedly tried to take Aleppo from the more moderate opposition groups, but largely failed. Now, along with the Syrian military, is also trying to seize the city.

“ISIS is so strong, especially with all the new weapons from Iraq,” Lattif said.

For the past month, ISIS has taken over large swaths of land in Iraq in an attempt to create an Islamic caliphate, which it declared last week, along with its name change to the Islamic State. It captured the town of Mosul June 10, taking control of heavy weaponry, which included Humvees, helicopters and rocket-propelled grenades.

Although these weapons have yet to be used successfully against the Iraqi military in Baghdad, they could be used in the battle for Aleppo.

After it took control of Mosul, ISIS bulldozed the border crossing between Iraq and Syria, allowing for the free flow of weapons and soldiers. That border crossing, Lattif said, has opened the road to Raqqa, an ISIS stronghold and what Lattif called the “ISIS capital.”

Lattif said Sunday the Dawood Brigade based in Idlib dispatched about 120 cars and tanks to Aleppo to support FSA battalions, but suddenly diverted them east toward Raqqa. Lattif said he thought the tanks went to support ISIS instead.

The constantly shifting alliances among the opposition have troubled U.S. senior politicians in the past and prevented them from sending heavier weaponry to the FSA to fight Assad’s forces. Last summer, President Obama announced the existence of a CIA-led program in Syria that would arm and train select opposition groups.

At the time of the announcement, many politicians claimed the administration did not have a good enough understanding of the opposition and the weapons could end up in the wrong hands. For months, amid escalating violence in Homs and Aleppo, the Obama administration refused to send heavier weaponry, such as portable anti-aircraft missiles, to Syria, fearing they would eventually be used against the West.

The opposition continued to ask U.S. and European leaders to pledge more arms and money to help fight Assad’s forces. That plea intensified as ISIS advanced in Iraq. Despite the requests, the U.S. has yet to send the weapons the opposition needs to win the war. Obama announced he would ask Congress for an additional $500 million to arm and train the moderate opposition in Syria but that assistance could take years.

“The program could work, but the problem is that it is complicated and it takes a long time,” said Mohammed Ghanem, a senior political adviser in Washington at the Syrian American Council, a grassroots organization based in Chicago. “Aleppo could be gone before then.”

According to activists in northern Syria, the opposition battalions in Aleppo have anti-tank weapons, such as RPGs, rocket launchers and machine guns.

“They are useless against the regime’s new tanks,” Lattif said. Last year, Lattif said, the military upgraded from T-72 tanks. The T-72 is a Soviet second-generation main battle tank. The newer tanks are thought to be stronger.

Ghanem said he has briefed several senior advisers in the White House about the need for heavier weapons in opposition battalions.

“What we are saying is that the president has … executive authority to help some of these groups so we can fight Assad and some of these extremist groups,” he said. “We need to do this now.”