BEIRUT: Syrian rebels knocked down army defenses and moved in on the country’s second-largest airport Wednesday, reportedly killing more than 40 soldiers and bringing them closer to what could be their biggest conquest since the start of the civil war.

Control of Aleppo international airport and a military air base next to it would be a huge strategic shift for Syria’s northeastern region, giving the opposition a potential air hub, enabling aid and other flights.

Still, activists said it could be days before the rebels would be able to push their way into the airport, 7 kilometers from the contested city center, and even then, it was unclear whether they would be able to retain control of the sprawling facility for long.

The country’s airspace is firmly controlled by the government, which uses its warplanes indiscriminately to bomb rebel strongholds.

The advance on the airport, which stopped handling any flights weeks ago because of the fighting, comes on the heels of other strategic gains. Rebels this week captured the nation’s largest dam and a military base near Aleppo. They have also brought the fight closer to Damascus, seat of President Bashar Assad’s regime, moving to within a few kilometers from the heart of the city.

“There have been some extremely significant advances by the rebels in the past few days. There is real fear and flagging morale among regime forces in the region,” said Muhieddine Lathkani, a London-based member of the Syrian National Council opposition group.

The government tried to reverse the gains with a series of airstrikes in several locations across the country Wednesday. In Jobar, a rebel stronghold in northeastern Damascus, 13 people were killed in government shelling, according to the opposition activist group the Syrian Observatory for Human Rights. Fighter jets also carried out airstrikes on rebel positions in the central province of Homs, it said.

The rebels have been pushing their way into the capital since last week. The foray marks the opposition’s second significant attempt to storm Damascus since July, when the rebels captured several neighborhoods before being swept out by a swift regime counteroffensive.

Since then, the regime has buckled down in Damascus, setting up checkpoints and controlling movement in and out of the city. The heavily defended capital so far has been spared the kind of violence that has devastated whole neighborhoods in other major cities such as Aleppo and Homs.

The rebels have had the most success in northern Syria, and have captured large parts of Aleppo, Idlib and Raqqa provinces since the conflict began.

Rebels have been attacking Aleppo’s civilian airport for weeks, and Tuesday overran large parts of the “Brigade 80” base that protects the facility.

By Wednesday, the Observatory said the rebels were “almost fully in control” of the base. Rami Abdel-Rahman, the group’s director, said over 40 regime troops had been killed in the fighting, including two brigadier generals, a colonel and two lieutenant colonels. An unknown number of rebels also died.

The base is about 2 kilometers from the civilian airport and the adjacent air base known as Nairab. Both have their own defenses in addition to the protection provided by Brigade 80. Lathkani said it would be one of the opposition’s most significant gains of the civil war if the rebels capture Aleppo airport, which according to its website is capable of handling 2.5 million passengers a year.

He said rebels were aiming to declare northern Syria a “liberated area” from which they would one day announce a transitional government.

“Aleppo airport would then be used for flying in aid, delegations and diplomats. It would serve as a hub for a self-administered area,” he said, but acknowledged concerns that the regime could bomb the runway to disable it.

The 23-month-old conflict in Syria has defied all international attempts to calm the bloodshed.

Russian Deputy Foreign Minister Mikhail Bogdanov said Wednesday that Syrian Foreign Minister Walid al-Moallem would travel to Moscow at the end of the month, the state RIA Novosti news agency reported. Bogdanov also said Ahmad Moaz al-Khatib, the leader of the Syrian National Coalition umbrella opposition group, is expected in Moscow “in the next two to three weeks.”

It was unclear whether the meetings were related to Khatib’s recent offer to hold talks with officials from Assad’s regime. Khatib has said he would be willing to meet outside the country or in “liberated areas” in northern Syria.

The Syrian Foreign Ministry issued a statement stressing that Moallem’s visit to Moscow had nothing to do with the coming trips by opposition groups to Russia, reasserting that any dialogue “must be on Syrian territory.”

In a speech at the Organization of American States in Washington, U.N. chief Ban Ki-moon urged the Security Council to overcome its paralysis and take meaningful action on Syria. “It is essential for the Security Council to overcome the deadlock and find the unity that will make meaningful action possible,” he said.

In Moscow, the head of Russia’s state arms trader said Wednesday it would continue to supply weapons to Assad’s government despite the escalating civil war.

Anatoly Isaikin, the director of Rosoboronexport, said that Russia sees no need to stop arms trade with Syria as it isn’t prohibited by the United Nations. Isaikin dismissed Western criticism of Russian arms sales to Damascus, saying that his company has delivered only defensive weapons. “In the absence of sanctions, we are continuing to fulfill our contract obligations,” Isaikin told reporters. “But these aren’t offensive weapons. We are mostly shipping air-defense systems and repair equipment intended for various branches of the military.

Also Wednesday, Syria’s former Foreign Ministry spokesman made his first comments since disappearing in December, saying he had left the country because “of the polarization and violence that left no place for moderation and diplomacy.”

Jihad Makdissi, who was known for defending Assad’s regime in fluent English, said in a statement sent to the Abu-Dhabi-based Sky News Arabia that he did not go to Europe or the U.S. after leaving Syria.