Activists and witnesses say army has been indiscriminately shelling Bab Amr neighbourhood of the city since Sunday.
The Syrian army has stepped up its attacks on opposition fighters in Homs, activists and witnesses have said, a day after a UN Security Council resolution, aimed at ending the bloodshed in Syria, was blocked by Russia and China.
Abu Abdo Alhomsy, an activist with the revolutionary council in Homs, spoke to Al Jazeera on Monday, describing an attack on the city as live pictures showed plumes of smoke billowing into the sky:
"It is horrible right here. Rockets are falling. There are massive explosions that shook buildings. We don't know really what to do," he said.
"Its a massive attack - a new massacre is happening here. Nobody can go out, we don't know how many homes have been hit or how many people died."
The Syrian revolution general commission said that 15 people were killed in Homs today, and at least three others were killed in Aleppo.
Video received by Al Jazeera from opposition activists on Sunday showed the apparent devastation caused by a military offensive in Bab Amr neighbourhood of Homs.
Activists and witnesses said the army had been shelling the neighbourhood "indiscriminately" since Sunday morning.
The video images appear to show people who have been shot and hit by shrapnel, including heavily injured young children.
Speaking to Al Jazeera, Danny Abdul Dayem, a resident of Homs: "It has been terrible. There is non-stop bombing with rockets, mortar bombs and tank shells. There were more than 50 people injured in Bab Amr today.
"I saw with my own eyes kids with no legs, and a kid who lost his whole bottom jaw. It is terrible."
In the northeast of the country, army deserters destroyed a military control post early on Monday, killing three officers and capturing 19 soldiers in the process, the Syrian Observatory for Human Rights said.
The fighting happened on the village of Al Bara in the Edleb region, the observatory said, adding that none of the army deserters involved was killed and that the regular army post was completely destroyed.
The death toll in Syria rose to at least 88 people over the weekend - one of the bloodiest since the uprising against Assad's government erupted almost 11 months ago.
Opposition groups say at least 6,000 people have now been killed in Syria.
Meanwhile, Europe is set to strengthen sanctions imposed on Damascus in a bid to boost pressure on the government, France said on Sunday.
"Europe will again harden sanctions imposed on the Syrian regime," French Foreign Minister Alain Juppe said on BFMTV television.
"We will try to increase this international pressure and there will come a time when the regime will have to realise that it is completely isolated and cannot continue."
Juppe also said France would "help the Syrian opposition to structure and organise itself" and would be working to create an international group on Syria.
uppe said French President Nicolas Sarkozy "will take steps in the coming days to try to bring together all those who consider the current situation (in Syria) absolutely intolerable".
He also described the veto by China and Russia as a "moral stain" on the United Nations and said France would consider a call by Tunisia for all countries to expel Syrian diplomatic envoys.
Juppe added, however, that a decision by France to expel Syrian diplomats could lead to a tit-for-tat expulsion by Damascus.
"It is possible of course, but it would have to be measured against the consequences because our embassy in Damascus is today also playing a humanitarian role," he said.
'Tragedy must stop'
Russia and China on Saturday blocked a UN Security Council resolution condemning Syria for its crackdown on protests, drawing condemnation from other global powers and the Syrian opposition.
Sergei Lavrov, the Russian foreign minister who will visit Damascus on Tuesday, has defended Moscow's decision to veto a draft UN resolution condemning the violence in Syria.
"Attempts to incite inter-ethnic or inter-religious contradictions or to start a civil war are totally unacceptable," he said after negotiations with Bahraini Foreign Minister Sheikh Khaled bin Ahmed Al Khalifa in Moscow on Monday.
Lavrov said adopting the resolution would have meant taking sides in a civil war, and he will ask Assad for rapid political reforms when he meets him.
The European Union has already agreed several rounds of sanctions against Assad's government, with dozens of government insiders and companies targeted so far by an assets freeze and travel ban.
The EU is also enforcing an arms embargo and a ban on imports of Syrian crude oil.
Since March 2011, "the Damascus regime has only responded to the legitimate aspirations of the Syrian people for freedom and democracy with fierce repression and endless promises," Sarkozy said.
Gerard Longuet, the French defence minister, earlier on Sunday criticised Russia for blocking the resolution on Syria and said Moscow could not hold out "indefinitely" in the face of global opinion.
"Russia, for reasons that are almost shameful, is blocking everything," Longuet told RTL radio.
"We have a duty, we Europeans, to show that we will never accept this regime. Russia can hold out for 15 days, two months, but it cannot hold out indefinitely," he said.