The head of the United Nations' peacekeeping operations has said that the situation in Syria now amounts to a full-scale civil war as witnesses on the ground described fresh shelling on Homs and heavy fighting in other cities.
"Yes, I think we can say that," Herve Ladsous, the head of the UN's Department of Peacekeeping Operations, told reporters in New York on Tuesday, when asked whether he believed Syria was now in a state of civil war.
"Clearly what is happening is that the government of Syria lost some large chunks of territory, several cities to the opposition, and wants to retake control."
Kieran Dwyer, a spokesman for the UN peacekeeping department, told Al Jazeera that Landous' description was "related to what is going on in the last five days."
"What we've seen in the last five days is a huge upscaling of the military confrontation," he said. "[It's by] both sides, at a huge cost to the civilian population."
His comments come as activists report heavy shelling in several districts in Homs in western Syria.
Residents of the Khalidiya neighbourhood told Al Jazeera that they had been trapped in their homes for the last three days without electricity or water.
Other neighbourhoods were reportedly targeted as well, and videos from the city, long a rebel stronghold, showed explosions in built-up areas.
Need of evacuation
Abo al-Barra, a doctor in Homs, told Al Jazeera that there were wounded civilians in need of evacuation. "They are severely injured," he said. "The women are badly injured, there are serious injuries."
The Associated Press news agency, meanwhile, reported heavy fighting in the eastern city of Deir Az Zor, where activists said at least 10 people were killed by artillery fire from the Syrian army.
Amateur video of the attack showed dead people in a street as survivors screamed in panic and tried to remove their bodies.
The UN mission in Syria posted this video, shot in and around Homs, which shows the aftermath of some shelling [UNSMIS]
The violence comes as President Bashar al-Assad's government faces mounting international pressure over brutal tactics against the opposition, with the UN reporting witnesses describing the use of children as human shields.
The UN report released on Monday also said children had been victims of detention, torture and sexual violence.
"The secretary-general expresses his deep concern at the dangerous intensification of armed violence across Syria over the past several days, and the grave danger facing civilians in areas under fire," Ban Ki-moon's office said in a statement.
"The bloodshed and fighting must stop at once."
Ban's criticism is based partly on reporting from the UN observer team on the ground in Syria, which also reported "planned and co-ordinated attacks [by rebels] on government forces and civilian infrastructure in multiple locations."
The UN has about 300 observers on the ground charged with monitoring both sides' compliance with a peace plan overseen by Kofi Annan, the former secretary-general turned UN envoy.
But the observers have been unable to reach certain parts of the country, including the coastal town of Haffeh, reportedly the site of heavy fighting in recent days.
The mission said it was barred from entering the town by "angry crowds" who threw rocks and metal rods at their vehicles.
"The security situation is not safe for them to enter," Sausan Ghosheh, a spokeswoman for the observer mission, told the Reuters news agency.
"They were at the last checkpoint and the government said, 'you can go through,' but we deemed it unsafe."
Fighters in the town said on Tuesday that hundreds of rebels were fighting a tank- and helicopter-backed assault on their district, which is tucked among rugged mountains.
In-depth coverage of escalating violence across Syria
Clashes started a week ago between rebels and security forces who were setting up checkpoints to tighten their grip on the strategic town, which lies close to the port city of Latakia as well as the Turkish border. It has allegedly been used by rebels to smuggle people and supplies.
The state-run SANA news agency said on Tuesday that security forces were continuing "persuasion of the remnants of the terrorists who committed vandalism acts and sabotaged public and private properties in al-Haffeh."
SANA quoted an "official source" who said that "a number of terrorists were killed and others wounded in the process" and "a number of terrorists" apprehended.
Victoria Nuland, a US state department spokeswoman, said Assad's forces were using "horrific tactics," including firing on civilians from airborne helicopters.
"This constitutes a very serious escalation," she said.
The Syrian foreign ministry responded in a statement on Tuesday, accusing the US of "flagrant interference in Syria's internal affairs."
The opposition says about 13,000 people have been killed since the uprising against Assad began in March 2011. Authorities say more than 2,600 members of the security forces have been killed.
Most accounts of violence cannot be independently verified, as Syria restricts access for journalists.