The Syrian government moved additional troops to Aleppo after clashes with rebels escalated in and around the country's largest city, a news report said Wednesday.
About 2,000 soldiers along with tanks and artillery were being moved from Idlib, 70 kilometers to the south-west, US broadcaster CNN quoted an official of the rebel Free Syrian Army as saying.
Fighting across Syria killed about 120 people Tuesday, the London-based opposition Syrian Observatory for Human Rights said.
An estimated 21 people were killed in Aleppo, the opposition Local Coordination Committees of Syria were quoted as saying by CNN. The group put Tuesday's country-wide toll at 133.
"Helicopter and tank shells are falling on areas in the outskirts of Aleppo, which came under the control of the rebels," activist Abu Haytham al-Halabi said by phone.
Government forces were seeking to quell a mutiny in Aleppo's central prison, where eight people were killed, the observatory said.
The Free Syrian Army described the mutiny as "the first step toward the liberation" of Aleppo.
US Secretary of State Hillary Rodham Clinton said Tuesday that the crisis in Syria was "accelerating" and that the opposition must ready for a post-Assad transition.
The offensive in Aleppo came as the Free Syrian Army warned that President Bashar Assad's regime had moved chemical weapons to airports, Qatar-based broadcaster Al Jazeera reported.
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