Syria's military has intensified its shelling of rebel-held areas of the city Homs, activists say, amid reports of aerial and ground bombardment elsewhere in the country.
Heavy clashes were reported between government forces and opposition fighters in Homs' al-Khalidiyeh neighbourhood, as videos posted online appeared to show barrels of TNT explosives being dropped on the besieged areas.
Opposition strongholds in Homs have been under siege for at least 120 days, with humanitarian conditions continuing to deteriorate.
Speaking to Al Jazeera, Raji Rahmet Rabou, an activist in Homs, said: "The siege is a huge problem for us. We are dying every day but nobody is paying attention to us.
"The last two days have been especially intense as the shelling did not stop whatsoever."
The northern province of Aleppo, eastern Deir Ezzor province and northwestern Idlib province also witnessed clashes between President Bashar al-Assad's troops and opposition fighters on Monday, activists reported.
In the southern province of Deraa, 20 people were reported killed in Karak al-Sharqi, including at least five rebel fighters, the UK-based Syrian Observatory for Human Rights said.
The observatory reported that some of the deaths came as troops blasted cars ferrying wounded people to field hospitals and clinics for treatment.
"Karak al-Sharqi has suffered repeated military assaults, heavy shelling and attempts to storm it over the past three days," said the observatory, which collates its information from a network of activists and medics on the ground.
It added that the town was facing "a crippling blockade and terrible medical and humanitarian conditions".
Monday's reported pre-dawn barrages came hours after a bomb exploded late on Sunday in a vehicle in the car park of the police headquarters in central Damascus, killing a policeman and damaging the building, state news agency SANA said.
Witnesses said that the blast was followed by heavy gunfire, while the observatory said "one or two people" were killed in the latest in a string of bombings of high-level security targets in the capital.
The latest reports of the violence in the country came as UN Secretary General Ban Ki-moon warned of a "dangerous fallout from spiralling violence along the Syrian-Turkish border".
"The escalation of the conflict along the Syrian-Turkish border and the impact of the crisis on Lebanon are extremely dangerous," Ban said at the opening of the World Forum for Democracy in Strasbourg, France.
The armed uprising has increasingly sparked violence on the Syria's border with NATO member Turkey, with the Turkish military returning fire on Sunday after a shell launched from Syria struck the border village of Akcakale.
There were no casualties in Sunday's incident, but last Wednesday five civilians were killed in the village following shelling from Syria.
'Abandon use of violence'
Since Wednesday, the Turkish military has responded in kind whenever Syrian ordnance has breached its territory, inflaming tensions between the former allies and leading to fears of a broader conflict.
Turkey's parliament on Thursday gave the government the green light to use military force against Syria if necessary.
In-depth coverage of escalating violence across Syria
The UN Security Council has strongly condemned cross-border attacks by Syria and called for restraint between the two neighbours whose relations have nosedived since the conflict began last year, with Ankara supporting the rebel fighters.
Shelling from Syria into Lebanon and cross-border shootings have become regular occurrences, while residents of Lebanon's frontier region accuse Syria's army of carrying out frequent incursions and kidnapping refugees.
The UN chief also raised concerns about arms supplies to both Assad's regime and rebel forces.
"I am deeply concerned by the continued flow of arms to both the Syrian government and opposition forces. I urge again those countries providing arms to stop doing so," he said.
"Militarisation only aggravates the situation. I am calling on all concerned to abandon the use of violence, and move toward a political solution. That is the only way out of the crisis."