WASHINGTON // The Syrian regime has moved some chemical weapons to protect them as it wages war against rebels forces, US defence secretary Leon Panetta said yesterday.
The main storage sites are not under threat but Mr Panetta said it was not clear if opposition forces battling Bashar Al Assad's rule have taken any of the weapons.
"We still believe, based on what we know and what we're monitoring, that the principal sites remain secure," he said. "I don't have any specific information about the opposition and whether they've obtained some of this or how much they've maintained."
Syria's chemical weapons stockpile dates back to the 1970s and are the largest in the Middle East, but its exact size is unclear.
Meanwhile, rebels yesterday launched a barrage of mortar fire against troops in Aleppo after announcing a "decisive" battle for the city, a rights group says.
The Damascus government has said it may use its chemical weapons if attacked by outside countries, but not on its own people.
Last month the French president, Francois Hollande, warned the use of chemical weapons by the Syrian regime would provide a legitimate cause for a foreign intervention.
The German magazine Der Spiegel reported on Monday that the Syrian army has tested a chemical weapons-delivery system, firing shells at a research centre in its north-western desert region.
Rebels claimed they had advanced on several fronts in Aleppo, particularly in the south-west, but admitted they had failed to make any significant breakthrough.
Some of the heaviest fighting took place for the first time in the predominantly Kurdish neighbourhood of Sheikh Maksoud. Kurds make up Syria's largest minority and have been divided in their loyalties.
The neighbourhood is mostly under the control of a pro-government Kurdish group. There were conflicting reports on whether Kurdish gunmen took part in yesterday's fighting.
"The city is witnessing one of the most violent days. All fronts are on fire," said Baraa Al Halabi, an activist in Aleppo, site of an intense two months of fighting.
Shells crashed down steadily and clashes were widespread, leaving layers of dust and smoke over Aleppo, residents and the Syrian Observatory for Human Rights said.
"The fighting is unprecedented and has not stopped since Thursday. The clashes used to be limited to one or two blocks of a district but now the fighting is on several fronts," the Observatory's Rami Abdel Rahman said.
Residents of neighbourhoods previously spared the violence called the fighting unprecedented.
"The sound from the fighting … has been non-stop," said Ziad, who lives in the central district of Sulimaniyeh. "Everyone is terrified. I have never heard anything like this before."
Abu Furat, one of the leaders of the Al Tawhid Brigade, said: "On the Salaheddin front we took one of the regular army bases.
But Mr Abu Furat admitted the fighters had to retreat from Salaheddin because they were outgunned.
"To win a guerrilla street war, you have to have bombs and we don't," he said.
The leader said 25 soldiers were killed in the assault, while another rebel fighter said 20 of his comrades died on the battlefield and 60 were wounded.
The Observatory gave initial estimates of 60 people killed across the country yesterday, half of them civilians, and said at least five civilians and five rebels died in Aleppo.
"We heard soldiers on their radio calling their chiefs to ask for reinforcements. They were crying and saying 'we are all going to die'," a rebel said.
Mr Abdel Rahman said: "Neither the regime nor the rebels are able to gain a decisive advantage."
Despite the violence, thousands of protesters took to the streets of Aleppo and other cities in support of the unification of the Free Syrian Army as splits appeared to undermine the revolt.
Government troops launched assaults on several rebel areas in the north of Damascus yesterday, the Observatory said.
"Regime forces stormed the neighbourhoods of Barzeh, Jubar and Qaboon in Damascus, cutting off streets and breaking into and raiding houses," it said. "They arrested a large number of residents."
Also yesterday, a Syrian shell crashed into a town on the Turkish side of the border, wounding a Turkish national, as fighting raged in a nearby Syrian town, a local official said.
The shell fired from the Syrian border town of Tall Al Abyad landed in Akcakale, in the province of Sanliurfa, smashing into the walls of two buildings and slightly wounding one person, the governor Celalettin Guvenc told the Anatolia news agency.
"I can clearly say the shelling did not target Akcakale," Mr Guvenc said, adding that Syrian shells sometimes ricocheted into the town.
The area was sealed off after the incident as security forces hunted for unexploded shells.
A week ago, the Turkish army deployed artillery and anti-aircraft missiles near Tall Al Abyad as a precautionary measure amid fighting in Syria for the control of the border post.
The UN top human rights body yesterday extended by six months the mission of its independent expert panel probing alleged war crimes in Syria's 18-month conflict.The panel led by Brazilian professor Paulo Sergio Pinheiro has blamed Syria's government forces for the majority of serious abuses since the uprising began in March 2011. Renowned former war crimes prosecutor Carla Del Ponte joined the UN inquiry into rights abuses, the UN Human Rights Council announced yesterday.
* Agence France-Presse with additional reporting by Associated Press