Syria rushes reinforcements to commercial capital Aleppo

BEIRUT — Syrian troops rushed dozens of tanks and reinforcements Wednesday toward Aleppo, the country's strategically vital commercial capital, in a bid to crush a rebel advance that has spread to wide swaths of the sprawling city.

As five days of fighting in Aleppo intensified, and with rumors swirling of a final showdown in that city, neighboring Turkey tightened its borders but said refugees will be allowed through.

"We are expecting a big attack on Aleppo," Mohammed Saeed, an activist based in Aleppo, told The Associated Press. "People are worried they might face random shelling while fleeing."

The rebels have made stunning advances over the past week, but the battle for control of Syria, a geographic and political linchpin at the heart of the Middle East, is far from over. And the potential for wider, regional unrest is great.

Israel's foreign minister warned that his country will act immediately if it discovers Islamic militants such as Lebanon's Hezbollah are raiding Syria's chemical or biological weapons stocks.

"For us, that's a casus belli, a red line," Avigdor Lieberman told Israel Radio.

Israeli officials have reported a run on gas masks. Demand has almost doubled in the past few days, to 4,200 requests on Tuesday from a years-old average of about 2,200, said Merav Lapidot, a spokeswoman for the Israeli postal service, which distributes the masks.

On Monday, Syria threatened to unleash its chemical and biological weapons if it faces a foreign attack.

The White House said Wednesday that the Syrian government's assault on Aleppo with tanks and fixed-wing aircraft illustrates what it called "the depth of depravity" by Assad's regime.

White House spokesman Jay Carney said the administration has seen "credible" reports about the regime's use of military hardware in Aleppo. Carney said Assad was using its forces to "perpetrate heinous violence" against the city's civilian population.