Syrian troops backed by Lebanon's Hezbollah entered Qusayr, a strategic rebel stronghold linking Damascus to the coast, a day after President Bashar al-Assad insisted he would not step aside. The advance Sunday came as Assad's opponents warned his regime's "barbaric and destructive" assault on the town could torpedo US-Russian attempts to organise a conference on ending more than two years of bloodshed. The Arab League called an emergency meeting for Thursday, ahead of the conference, as the opposition Syrian National Council (SNC) demanded that it meet and "stop the massacre in Qusayr". Loyalist forces launched the offensive with a heavy early-morning bombardment using artillery and warplanes. "We struck from several fronts -- south, east and northeast," one soldier told state television from the rebel bastion. After fierce fighting the army quickly seized the southern part of town, the town hall and nearby buildings, and advanced on the western outskirts, he added. He said that "100 armed men were killed" in the operation during which troops had to defuse mines and bombs placed by rebels at the gates of the town. A military source told AFP that government forces controlled the centre of Qusayr and that the Syrian flag was flying over the recaptured municipality building. The Syrian Observatory for Human Rights watchdog confirmed the bombardment and the subsequent ground operation. Observatory chief Rami Abdel Rahman told AFP that Hezbollah militants from Lebanon were "playing a central role". "If the army manages to take control of Qusayr, the whole province of Homs will fall," he said. The Britain-based Observatory reported more air strikes later Sunday, saying at least 52 people had been killed during the day, including at least 21 rebels and three women. The regime has made recapturing Qusayr and the surrounding district of Homs province a key objective, and fighting has raged in the region for months. In recent weeks, government troops backed by Hezbollah and members of the National Defence Forces, a pro-regime militia, have taken a string of villages as they moved in on Qusayr. A source close to Hezbollah told AFP in Beirut that four of the group's members had been killed overnight shortly before the assault on Qusayr began. The fighting has also spilled over into neighbouring Lebanon. The National News Agency in Beirut said eight rockets fired from Syria hit Lebanon, without causing casualties or damage. The SNC, a key component of the main opposition National Coalition, denounced the "barbaric and destructive bombing" of Qusayr. It accused the regime of working with Hezbollah to "invade the town and wipe it and its residents off the map", and called for "an urgent meeting of the Arab League to stop the massacre in Qusayr". "We say to the countries that are working for a political solution in Syria that allowing this invasion to go ahead in silence... will render any conference and any peace effort meaningless." UAE Foreign Minister Sheikh Abdullah bin Zayed al-Nahayan also called for "the repressive machine in Damascus" to be stopped. France also expressed fears for civilians, with foreign ministry spokesman Philippe Lalliot calling on Sunday for "all the players in a position to avoid a new massacre of the Syrian civilian population to mobilise without delay". More violence would only undermine the peace process, he added. The United States and Russia are working to organise a peace conference next month to find a political solution to the conflict. While Washington has backed the uprising against Assad, Moscow is one of his staunchest allies. But the embattled Syrian leader said in a weekend interview with Argentine newspaper Clarin that he would not resign before the end of his mandate in 2014. The Syrian military was advancing on other fronts on Sunday, taking control of the rebel-held village of Halfaya in Hama province, the Observatory said. State television reported the army had killed numerous members of the Al-Nusra Front in Halfaya, referring to a jihadist group branded as "terrorist" by the United States. In Damascus, a military source said troops were advancing in the Barzeh district on the northern outskirts of the city. The UN says that more than 70,000 people have been killed since the anti-Assad uprising erupted in March 2011, but the Observatory puts the death toll at around 94,000.