Aleppo bomb
Children walk on rubble as civilians inspect a site hit by what activists said was a missile fired by forces loyal to Syria's President Bashar al-Assad at Aleppo's Bab al-Nairab district August 11, 2014. Reuters/Rami Zayat

As ISIS militants find themselves under U.S. airstrikes in Iraq, their brethren fighting for the Sunni militant group in Syria are taking towns in the northern part of the country with ease -- and they could find themselves as the dominant opposition force around the nation's biggest city.

Since Wednesday, ISIS has seized Turkman Bareh, Akhtarin, Dabiq, al Masoudia and al Ghouz in northern Syria. ISIS has been operating in northern Syria for months, but made new advances toward Aleppo, the country’s economic hub, in an attempt to confront regime forces that have encircled the city from the south and east. ISIS advances indicate that another battle for Aleppo could begin within the next few days, according to activists on the ground there.

Despite ISIS gaining ground north of Aleppo, a major battle between the regime and opposition forces has yet to break out. The first battle for Aleppo, which took place in August of 2012, was between forces loyal to President Bashar al-Assad and militias fighting under the umbrella of the Free Syrian Army (FSA). A battle for Aleppo today, though, is more likely to include fighting between the regime and ISIS.

The ISIS consolidation in the north is pushing out other opposition groups such as Jabhat al-Nusra (or al-Nusra Front), linked to al-Qaeda, and the FSA from the area. If the FSA lost its hold on areas around Aleppo, it would mark the biggest blow to the moderate opposition, backed by the West, since the beginning of the war more than three years ago. The FSA has already lost Homs, which was once considered the “heart of the revolution.” If it lost Aleppo, a trade hub and the largest city in the country, it would risk losing control of towns along the border of Turkey, its main transit route for fighters and weapons.

According to the British Observatory of Human Rights, one of the few independent monitoring groups in the country, as of Wednesday afternoon ISIS had taken over several villages in Aleppo's northeastern countryside. The takeover of the towns came after intense battles between the Sunni militant group, which has also taken over large swaths of land in Iraq and declared an Islamic Caliphate, and other Muslism militant forces such as Jabhat al-Nusra.

According to reports from Syrians on Twitter and from the British Observatory of Human Rights, ISIS captured the town of Akhtarin, which opens the doors to Mare and Az’az near the border with Turkey. Fighters from the Dawoud Brigade, which pledged allegiance to ISIS last month, provided military vehicles for the group. Later in the day, ISIS and its supporters began firing shells into neighborhoods on the outskirts of Aleppo.

According to the British group, as ISIS advances the regime has begun to hit some Aleppo neighborhoods and towns north of the city with barrel bombs, crude but devastating devices dropped from helicopters. From information provided by activists on the ground, the regime is not discerning in its attacks between ISIS and other opposition groups. On Thursday it dropped bombs on towns under control of both ISIS and al-Nusra.

It is unclear if ISIS has been able to move to the weapons and tanks it seized from the fleeing Iraqi Army when it took over Mosul, Iraq’s second largest city, June 10. After Mosul, ISIS militants bulldozed the border between Iraq and Syria to allow for the free flow of soldiers and weapons, but most of those weapons have been seen on the ground in Iraq as ISIS tries to move closer to Erbil in Iraqi Kurdistan.

Activists and fighters with the FSA said they have been preparing for a battle in Aleppo for more than a month. After taking over the town of Al Bab more than five months ago, ISIS has slowly made advances toward Aleppo, and tried to take the town of Akhtarin from moderate opposition groups in July. FSA supporters who used to live in Al Bab have now fled to border towns in Turkey.