Rebels close in on Syrian capital of Damascus

(CBS News) LONDON - In Syria, two car bombs exploded Sunday in the city of Homs.

At least 15 people were killed and dozens of others wounded. Fighting also intensified around Damascus and rebels are closing in on the capital.

In Damascus, the explosions are getting louder, fighter jets are flying closer. The 20-month old war has reached the city's suburbs.

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For the first time, rebels are challenging the Syrian Army for control of the main airport. Street battles have grounded flights for three days. Rebels have also taken control of two military bases, and appeared to be planning a push into the center of Damascus.

Assad's Army answered with rockets and bombs Sunday. So far, the regime has managed to stop an attack on the city and retain control of the airport. But for how long?

"The rebels have been able to harass the capital as well as its supply chain for several days and this is unprecedented in the history of Syria," said Andrew Tabler, an analyst at the Washington Institute for Near East Policy. "It's another sign that the Assad regime is going to contract and perhaps on the way out."

The last time rebels tried to fight their way into the capital in July, the Assad regime moved its forces out of cities in the north and south to reinforce Damascus. It worked.

This time, rebel groups have anti-aircraft weapons and claim to have shot down a government attack helicopter. That kind of firepower, analysts say, is what the Free Syrian Army needed to gain ground against the regime.

But Assad has a weapon of last resort -- chemical weapons.

"They have the largest stockpile in the Middle East," said Tabler. "It's weaponized. There are an estimated 45 sites throughout the country."

Tabler says if Assad is backed into a corner, he just may use them.