At least two top commanders in the Northern Storm Brigade have been wounded. Their loss has propelled Abu Marwan, a surprisingly shy pilot in his 20s who defected from the Syrian military more than a year ago, into a top leadership position.

"I may be the youngest fighter in the group," the former lieutenant said with a smile, after declining to reveal his exact age.

Videos secretly filmed by opposition activists show Syrian soldiers almost casually walking around tanks and tents in the airbase.

Last Sunday, rebels said the defenders broke through the siege lines to receive a much-needed delivery of supplies under cover of darkness. First, warplanes roared overhead, they said, sending people running for cover. It was then that a helicopter flew in, picked up wounded soldiers, and dropped off supplies before leaving.

A special forces soldier who escaped from the base and surrendered to rebels last week told CNN the troops inside were segregated between mostly Sunni Muslim foot soldiers like himself and officers who were predominantly Alawite, the same religious minority as Syrian president Bashar al-Assad.

"They discriminate between the Alawites and Sunnis," said the soldier, a 22-year-old man from the southern city of Deraa, who asked not to be named.

"The Sunnis go to the front almost as if they are human shields ... and all the Alawites stay behind."

The soldier said there were large stores of food and even supplies of electricity for commanders.

As for weapons, "we have so many weapons at the airport I can't even count. But despite that I could (see) that (the rebels) are not afraid."

The siege forces appear to have received fresh reinforcements in past weeks.

Last weekend, a CNN team of journalists traveled towards the front lines escorted by a young activist from an opposition media center in the nearby anti-regime town of Azaz.

Shortly after passing a line of bombed out buses and trucks serving as a barricade, the reporters were intercepted by a small group of fighters, who covered their faces once they spotted cameras.

"I am very sorry that you traveled all this way, but you have to leave," their hooded leader explained politely, yet firmly, in fluent English. "This is a restricted military zone."

The guide from the Azaz Media Center later explained that the fighters were members of an Islamist rebel group affiliated with the Muslim Brotherhood. He said another group of fighters spotted around several parked pickup trucks were members of al-Nusra Front.

Last month the U.S. government blacklisted al-Nusra, declaring it a terrorist organization linked to al Qaeda. However, al-Nusra rebels continue racking up victories on the battlefield and appear to be attracting growing respect from many supporters of Syria's weary armed opposition.

Streaming out of Syria

Syrians and foreigners continue to flee the fighting.

Nearly 5,900 refugees entered neighboring Jordan over the previous 24 hours, the kingdom's state-run news agency, Petra, reported Tuesday. Border guards gave the refugees humanitarian aid and took them to Zaatari refugee camp.

Russia was planning to fly out about 80 of its nationals who have managed to leave Syria, government officials said, according to RIA Novosti. Two planes arrived in Beirut from Moscow to evacuate the Russian nationals, who have made their way to Lebanon.

"The group includes Russian women who have married Syrians, their children and husbands who have acquired Russian citizenship," RIA Novosti said, adding they will be flown to Moscow.

At least 51 people died in the civil warfare on Tuesday, the opposition Local Coordination Committees of Syria said.