Syrian troops have reportedly clashed with opposition fighters in the city of Homs, as the army tried to enter the opposition stronghold of Bab Amr.
Opposition activists said the fighting happened at the al-Bassel football field at the outskirts of Bab Amr, which is controlled by the armed opposition. Heavy fighting was reported in the area on Wednesday.
There were reports that elite troops of the Fourth Armored Division, commanded by President Bashar al-Assad's brother, Maher, had deployed with tanks around Bab Amr.
Activists said Syrian soldiers also abandoned checkpoints in the northern part of Homs, in the neighborhoods of Al-Khaldia and Bayada.
They then started a heavy shelling campaign. There have been reports of sporadic shelling of other opposition areas in and around Homs.
"Homs is now and today experiencing the worst crackdown from al-Assad batallions and Assad regimes and every district and residential area in Homs is being surrounded," Hadi Abdullah, an activist in Homs, told Al Jazeera on Wednesday.
"The Syrian army is using all the weapons and we are really scared because we can safely say that these areas will be a traget of severe shelling from the Syrian army."
Soldiers are reportedly also searching houses and other buildings for army deserters who have since joined the opposition Free Syria Army.
"It is obvious that they are launching a major offensive against the strongholds of the Free Syria Army," said Al Jazeera's Rula Amin, reporting from neighbouring Lebanon.
"President Assad and the government have made it clear, he has said that he wants this month to be a decisive month. They believe that in this month they can contain the opposition, they can crush the armed opposition and that's what they are trying to do."
Amin said sources close to the government said the army had almost cleared Bab Amr from fighters, but this claim was disputed by activists.
The latest reports of violence came as the international community continued to debate the Syria crisis.
UN humanitarian chief Valerie Amos on Wednesday said Syria has denied her repeated requests to visit the country.
Amos said in a statement that she is "deeply disappointed" that Syria turned down her requests to meet officials at the highest level "to discuss the humanitarian situation and the need for unhindered access to the people affected by the violence".
In-depth coverage of escalating violence across Syria
She said given the rapidly deteriorating humanitarian situation, improved access was "a matter of the highest priority".
Kofi Annan, the UN-Arab League envoy for Syria, meanwhile planned to hold talks in New York from Wednesday through Friday with UN Secretary-General Ban Ki-moon and member states on Syria.
The Chinese foreign minister on Tuesday said his country would back international efforts to send humanitarian aid to Syria, after Western powers proposed a United Nations resolution authorising humanitarian aid.
"The pressing task now is for all sides to cease violence in the Syrian conflict, and to launch as soon as possible inclusive political dialogue and together deliberate on a reform plan," Yang Jiechi told Nabil Elaraby, the head of the Arab League, during a phone call late on Tuesday.
"The international community should create conditions for this, and extend humanitarian aid to Syria," Yang was quoted as saying by the official Xinhua news agency.
It was not clear whether Yang's remarks meant China would consider the proposed new UN Security Council resolution.
China has been widely condemned for its handling of the Syria crisis. Elaraby has previously said Beijing lost diplomatic credit in the Arab world after it joined Russia in vetoing two previous Security Council resolutions.
The US has drafted an outline for a new resolution demanding access for humanitarian aid workers to besieged towns and an end to the violence there.
Arming the opposition
The UN estimates that more than 7,500 people have been killed by Syrian President Bashar al-Assad's forces since the start of the uprising in March last year.
"There are credible reports that the death toll now often exceeds 100 civilians a day, including many women and children," said Lynn Pascoe, the UN's under-secretary-general for political affairs.
Syria's government said in December that "armed terrorist groups" had killed more than 2,000 soldiers and police. Scores of troops have since been reported killed.
Syria's Foreign Ministry Spokesman Jihad Maqdisi said in a news conference on Wednesday that calls for arming the country's opposition constituted an aggressive act against his country.
"Any party that issues such declarations will carry the political responsibility for the bloodshed of Syrians," he said.
Maqdisi said that an announcement by Qatar officials calling for the arming of Syria's opposition is nothing new and affirmed that "arming the opposition will harm any legitimate demands of the people - to which," he claimed, his government "is willing to respond".
The White House earlier said al-Qaeda's efforts to take advantage of the violence in Syria meant it was not the time to begin sending arms to opponents of Assad.
"Now is not the time to further militarise the situation in Syria," said Jay Carney, the White House spokesman. He said applying political pressure on Assad to leave office and to cease the military crackdown on dissidents was a better option than sending in weapons.
Navi Pillay, the UN human rights chief, said during an emergency debate on Tuesday at the Human Rights Council that the world has to take action to prevent Syrian security forces from continuing their bombardments and other attacks against civilians, which she said had resulted in "countless atrocities".
Pillay said the situation in Syria had deteriorated rapidly in recent weeks and called for an immediate humanitarian ceasefire. Activists said scores more people were killed across the country on Tuesday.
Pillay's appeal prompted a bitter response from Syria's ambassador to the UN offices in Geneva, who accused the 47-nation council of promoting terrorism in his country.
Before storming out of the room, Faysal Khabbaz Hamoui, said the debate, which is due to continue on Thursday, would only prolong the crisis in Syria.