BEIRUT, Lebanon - Syria's civil war is closing in on President Bashar al-Assad's seat of power in Damascus with clashes between government forces and rebels flaring around the city Tuesday, raising fears that the capital will become the next major battlefield in the 20-month-old conflict.

Numerous reports emerged of at least a dozen people killed near the ancient city and elsewhere, and the regime said nine students and a teacher died from rebel mortar fire on a school. The state news agency originally said 30 people had been killed in the attack.

While many of the mostly poor, Sunni Muslim suburbs ringing Damascus have long been opposition hotbeds, fighting has intensified in the area as rebels press a battle they hope will finish Assad's regime.

"The push to take Damascus is a real one, and intense pressure to take control of the city is part of a major strategic shift by rebel commanders," said Mustafa Alani of the Geneva-based Gulf Research Center. "They have realized that without bringing the fight to Damascus, the regime will not collapse."

The increased pressure has raised worries that he or his forces will resort to desperate measures, perhaps striking neighbors Turkey or Israel, or using chemical weapons.

On Monday, President Obama said there would be consequences if Assad made the "tragic mistake" of deploying chemical weapons, and Israeli Prime Minister Benjamin Netanyahu said he agreed with the U.S. position.

"We are of the same opinion, that these weapons should not be used and must not reach terror groups," Netanyahu said.

U.S. intelligence has seen signs that Syria is moving materials inside chemical weapons facilities recently, though it is unsure what the movement means.

In July, Foreign Ministry spokesman Jihad Makdissi told a news conference that Syria would only use chemical or biological weapons in case of foreign attack, not against its own people. The ministry then tried to blur the issue, saying it had never acknowledged having such weapons.

On Monday, Lebanese security officials said Makdissi had flown from Beirut to London. He has not spoken publicly in weeks and it was unclear whether he had left the government.

Rebel groups around Syria have scored victories in recent weeks, overrunning military bases and airports and halting air traffic at the capital's international airport for days.

Most analysts agree that the tide is turning, however slowly, against the regime.

But Fyodor Lukyanov, editor of the foreign policy magazine Russia in Global Affairs, said Assad won't leave without a fight.

"Assad realizes that there is no way back for him," said Lukyanov, a leading Russian foreign policy expert with high-level Foreign Ministry connections. "If he tries to jump the boat, his own supporters will not forgive him for doing that. And if he loses, no one will give him any guarantees."