(CNN) -- Violence surged in the strategically important Syrian town of Qusayr on Sunday. Activists said the offensive marked some of the most intense fighting they've seen in the fiercely contested area near the Lebanese border.
Rebels and the Syrian government both claimed to control parts of the city, where fighting has been raging for weeks. Activists said artillery shells, mortar shells and bombs from aircraft were raining down as government forces attacked. Makeshift medical clinics were reportedly filled with casualties.
By all accounts, Qusayr is in a strategically valuable location.
For rebels fighting President Bashar al-Assad's government, it sits along a transit route for weapons and supplies coming in from Lebanon.
For the Syrian government, it's a key point between the capital of Damascus and al-Assad's supporters on the Mediterranean coast.
Videos posted on social media Sunday show the city blanketed with black and gray smoke amid an almost continuous stream of sounds of mortar and artillery fire.
Dozens of people were killed in the clashes, including 48 rebel fighters, the London-based opposition Syrian Observatory for Human Rights reported.
Hundreds of people were injured, many in critical condition, the opposition organization said.
Syrian state-run television reported that Syrian forces "have spread safety and security after taking control of the city hall and surrounding buildings in Qusayr as they continue to chase the terrorists in the city."
The opposition Local Coordination Committee of Syria denied that report.
"The field commanders in the Free Syrian Army stress that they remain in control of the city and are fighting back attempts to storm the city," the opposition activist network said in a statement.
Activists describe a city under siege
Qusayr has been under rebel control for months.
The opposition accused Hezbollah fighters from neighboring Lebanon of joining Syrian government troops in the assault on the city, a claim that al-Assad's government has disputed in the past.
The Shiite militant group is considered a terror organization by the U.S. government and is a traditional ally of al-Assad as well as Iran.
The Free Syrian Army said it fired rockets from Qusayr across the border into northeastern Lebanon, targeting Hezbollah areas. The official Lebanese news agency said eight rockets landed in Hermel.
Activists in Qusayr said the city was under siege Sunday from several directions.
"There is continuous shelling using artillery, mortar and warplane bombs," activist Abu Ali said. "It is so intense, like 50 shells a minute."
Residential areas were hit, said Abulhoda Homsi, another activist.
The opposition Syrian National Council warned that 40,000 civilians' lives were in danger amid the violence and called for the Arab League to hold an emergency meeting to protect the besieged city.
The United Nations estimates that more than 70,000 Syrians have been killed since anti-government protests in March 2011 led to a fierce government crackdown, an armed uprising and a civil war with no end in sight. At least 125 people were killed across the country Sunday, the Local Coordination Committees reported.
The voice of Assad
In an interview with Argentine journalists on Saturday, Assad said Syria can solve its own problems.
"It isn't up to the United States or any other country to intervene," the Syrian president told Argentina's Telam news agency. "This is an issue that is Syrian. We are an independent state. We respect ourselves. We don't accept anyone telling us what to do -- not the U.S., not any other country."
Assad asserted he's dealing appropriately with people he calls "terrorists."
"Nobody has dialogue with the terrorists. Terrorism has hit the United States and Europe. By any chance, did any of these governments talk to terrorists? One talks with political entities, but not with a terrorist who cuts people's throats, assassinates people and uses chemical weapons," he said, ignoring allegations that his own government has very likely used chemical weapons on Syrian citizens.
The Syrian civil war has uprooted a quarter of the country's civilians, according to the United Nations.
The number of Syrians who have fled the violence has surpassed 1.5 million, the U.N. High Commissioner for Refugees said Friday.
Since the start of 2013 alone, the UNHCR has registered close to 1 million refugees crossing out of the battered nation into other countries, which amounts to about 250,000 people each month.
Along with the refugees, more than 4 million people have been internally displaced.
Syria has a population of just over 22 million, according to the CIA World Factbook.
CNN's Yousuf Basil, Samira Said and Nic Robertson contributed to this reoprt.