BEIRUT (AP) -- Government troops launched a series of attacks in central Syria Saturday, striking with artillery, tanks and warplanes in a drive to capture rebel-held neighborhoods in the country's third largest city of Homs, with activists said.
The army of President Bashar Assad has been on the offensive in Homs province in recent weeks, reclaiming some of the territory it has lost to the rebels since Syria's crisis began 27 months ago.
The military, building on its capture of the strategic town of Qusair between the Lebanese border and Homs at the beginning of this month, has overrun a number of nearby villages. It also has hammered the center of the city, a rebel stronghold since the uprising against Assad began in March 2011.
Homs, a city of about 1 million, has shown great sympathy for the opposition since the early days of the uprising. A month after it started, protesters carried mattresses, food and water to the main Clock Square, hoping to emulate Cairo's Tahrir Square, the epicenter of Egypt's revolt that overthrew Hosni Mubarak.
Security forces quickly raided the encampment, shooting at protesters and chasing them through the streets. The onslaught only boosted the intensity of the protests, fueling a revolt that has posed the most serious challenge to date to the Assad family dynasty that has ruled Syria since 1970.
Homs is the capital of Syria's largest province, which carries the same name and stretches from the Lebanese border to the frontier with Jordan and Iraq.
Activists in the city said all cellular lines were cut early Saturday before warplanes pounded rebel-held areas. The air raids were followed by intense shelling with artillery, mortars and tanks, before troops tried to advance.
Several activists in the city said the regime began bringing in reinforcements since last week, apparently in preparation for the attack.
Two activists said about 400 shells struck rebel-held areas such as Qusour, Jouret el-Shayah, Old Homs and Khaldiyeh.
"This is the worst campaign against the city since the revolution began," said an activist in the rebel-held old quarter of the city via Skype. "They are using all types of weapons," said the man on condition of anonymity for fear of government reprisals.
The Britain-based Syrian Observatory for Human Rights said air strikes hit two districts in the center of the city. It said the army also fired mortar shells into the neighborhoods.
An activist from the neighborhood of Khaldiyeh said tanks were also involved in the bombardment, and that the military was trying to push into the area from all sides.
Shelling has been continuous since 10 a.m. in that area and in nearby Old Homs, activist Tariq Bardakhan told The Associated Press via Skype.
"Today is one of the most violent days that Homs has witnessed since the beginning of the revolution," he said.
In an activists' video of the bombardment, several large explosions can be heard as plumes of grey smoke rise from buildings in a densely built-up area of the city.
The narrator of the video says: "These are heavy explosions that hit Homs, God is great." Another shell lands and smoke can be seen rising from behind a mosque. Two minarets are seen in the distance and the narrator says they belong to the historic Khalid Ibn al-Walid mosque in Khaldiyeh.
The video was posted on the Internet on Saturday and appears consistent with AP's reporting from the area.
The Observatory confirmed clashes around the mosque, and said that part of the building, which dates back to the 13th century and has been damaged in previous fighting, was engulfed in flames. It added that troops tried to storm the mosque with no success.
The Observatory said both sides have sustained casualties, but did not have numbers.
Syrian state TV said the army has had "great success" in the battle for Homs after "killing many terrorists in the Khaldiyeh district."
Syrian state media refers to rebels fighting to oust Assad from power as "terrorists" and say they are mercenaries of the West and their Gulf Arab allies who are conspiring against Damascus.
Before the fighting moved to the capital Damascus and the northern city of Aleppo in July last year, Homs was the center of the uprising and became known as "the capital of the Syrian revolution."
Rebels received a major blow in March last year when troops captured the Baba Amr neighborhood after weeks of fighting that left scores dead. Among those killed in Baba Amr last year were French photographer Remi Ochlik and Britain's Sunday Times correspondent Marie Colvin.