Syrian rebels making a push against troops in Syria's most populous city are meeting with stiff resistance as the death toll rises.

Rebel leaders began an offensive in the commercial hub of Aleppo late Thursday, one commander told his brigade.

''Allahu Akbar (God is the greatest), the start of the decisive battle in Aleppo and those are the heroes of Al Tawhid battalion starting to deploy in the streets of Aleppo, God willing.”

Videos posted on the Internet showed scenes of running street battles and mortar fire. But by midday Friday, rebel commanders in contact with the media were reporting little progress.

Violence also raged in the capital of Damascus, where troops loyal to Syrian President Bashar al-Assad stormed several districts looking for rebels and rebel sympathizers.

On the Turkish border, at least one mortar shell from Syria smashed into a home in the Turkish town of Akcakale. No injuries were reported.

Despite the violence, amateur video showed hundreds of Syrians taking to the streets in parts of Aleppo, Damascus and other cities, in a show of support for rebel forces.

During a briefing at the Pentagon, U.S. Defense Secretary Leon Panetta said there is evidence the Syrians are worried some of their chemical weapons might be vulnerable.

“There has been some intelligence, that in regards to some of these sights, that there has been some movement for the Syrians to better secure the chemicals.”

Panetta said Friday the major chemical weapon stockpiles appeared to be intact, but that concerns remain.

“But as to the movement of some of these materials and whether or not they've been exposed to possession by the opposition or others, that's something I don't really have firm information on.”

Meanwhile, the United Nations human rights council Friday expressed renewed concern about abuses by both government and rebel forces, extending the mandate of its war crimes inquiry by six months.

The U.S. ambassador to the council, Eileen Chamberlain Donahoe, says the situation in Syria is dire.

“Assad continues to cling to power and his campaign of brutality has sparked a deepening humanitarian crisis. We cannot afford to be silent.”

The council also appears poised to take an even harder line against the abuses in preparation for potential war crimes trials.

Several diplomats said Friday the council was preparing to appoint the former chief prosecutor of the International Criminal Court to the investigative team.

Carla del Ponte served on the ICC prosecuting crimes in the former Yugoslavia until January 2008.

The investigation has already interviewed more than 1,000 victims, refugees and defectors but has not been granted access to Syria itself.

Also Friday, selected members of the Friends of Syria group is scheduled to meet in New York, hosted by U.S. Secretary of State Hillary Clinton. It will include ministers from more than 20 nations and representatives from local revolutionary councils.

A senior State Department official said the meeting, which takes place on the sidelines of the U.N. General Assembly, will focus on support to the Syrian opposition, humanitarian assistance and international pressure on the Syrian regime.

The official says the discussions will include unilateral measures which can be taken against the regime including the possibility of sanctions.