Syria warned Tuesday it is ready to fight "for years" against rebels, as world powers worked on a new initiative to find regime officials suitable for peace talks with the opposition.
The UN children's agency UNICEF said an entire generation risked being lost in the spiralling conflict between President Bashar al-Assad's forces and insurgents.
As the bloodletting approached a third year without a solution in sight, France said it was working with Russia and the United States to draw up a list of regime officials with whom the opposition can negotiate.
French Foreign Minister Laurent Fabius said "we worked together on an idea... of a list of Syrian officials who would be acceptable to Syria's opposition National Coalition."
Opposition chief Ahmed Moaz al-Khatib has offered to talk to regime representatives without "blood on their hands."
Britain said it would consider ignoring a European Union arms ban and could supply weapons to rebels if it would help topple Assad.
Prime Minister David Cameron said he hoped London could persuade its EU partners "if and when it becomes necessary (to provide weapons) they'll agree with us."
Last month, the EU amended its embargo to allow members to supply "non-lethal" equipment and training to the opposition but stopped short of lifting the embargo entirely.
Asked whether Britain would veto the arms embargo when it comes up for renewal in three months, Cameron told a parliamentary committee he would "like to continue with an EU approach."
"But if we can't, then it's not out of the question we might have to do things in our own way. It's possible.
When asked if arming the rebels could be risky, he replied: "That is not a decision we've taken and I hope we don't have to break from a collaborative approach across the EU.
"I was just making a point that if we thought that was the right thing to do, we would do it."
The EU is split over arming the rebels. Britain, France and Italy are tipping in favour of it, while Germany and others warn against it.
On the ground, rebels and troops fought fierce battles over the contested district of Baba Amr in third city Homs, and clashed on the road linking Damascus to the international airport.
Pro-government newspaper Al-Watan said the army was "in perfect condition" and that it "has at its disposal enough men and weapons to fight for years to defend Syria".
Syria "is in a state of war" and "facing a real invasion," it said, stressing citizens could also join in the battle.
Assad's regime, which has consistently blamed foreign powers for the violence, also sent letters to the UN urging "pressure on certain Arab and Western countries that supply aid to terrorism."
In Homs, fighting focused on Khaldiyeh, with regime forces backed by tanks pounding the northern district.
"Troops launched rockets from the Baath University into parts of Baba Amr," said the Syrian Observatory of Human Rights.
Battles also raged on the road linking Damascus to the airport, said the watchdog. Rebels have been trying to seize control of the road for months.
The Observatory said 77 people had died in violence across Syria on Tuesday.
In Geneva, UNESCO sent out an SOS that a whole generation of Syrian children could disappear.
"As the crisis in Syria enters its third, tragic year without any end in sight, the risk of a lost generation grows every hour, every day and every month," UNICEF spokesman Patrick McCormick said.
"We cannot afford to lose any more time. We certainly cannot afford to lose another year. We risk creating a generation of children who have seen, or know, only fighting, and may well end up perpetuating that cycle of violence."
UNICEF pointed out that nearly half of the four million in dire need of aid inside Syria are under the age of 18, and 536,000 of them are children under five.
Russia meanwhile delivered 10 tonnes of aid to Syria, SANA news agency said, and evacuated 103 citizens from the country, according to news reports from Moscow.