Fierce fighting rocked northern Syria on Friday as neighbouring Turkey kept up its calls for internationally protected safe havens inside the violence-ridden country to stem the huge outflow of refugees.
UN chief Ban Ki-moon told Syria's premier in Tehran that Damascus must stop using heavy weapons in the conflict, and the International Committee of the Red Cross warned of a fast deteriorating humanitarian situation.
Clashes erupted in the battleground city of Aleppo, less than 50 kilometres (30 miles) from the Turkish border, and rebels attacked the Abu Zohur air base in Idlib province on the border where they said they shot down a MiG warplane on Thursday, a rights group said.
Turkish Foreign Minister Ahmet Davutoglu expressed frustration at the reluctance of Ankara's Western allies to heed its calls for protected camps inside Syria to cope with the rapidly swelling numbers of fleeing civilians.
The United Nations estimates that in Aleppo alone at least 200,000 of the city's 2.7 million population have fled since it became a major battleground on July 20.
Rebels attacked a security service building in west Aleppo before dawn, and clashes erupted in the districts of Saif al-Dawla and Salaheddin in the southwest and Hanano in the northeast, the Syrian Observatory for Human Rights said.
In Idlib province, rebels seized part of the Abu Zohur base in heavy clashes, the Britain-based watchdog said.
The rebels say that aircraft from Abu Zohur have been used by President Bashar al-Assad's regime to launch devastating strikes on rebel-held areas, and on Thursday a Free Syrian Army commander said the FSA had downed a MiG based there.
The regime has not commented on the claim.
The Abu Zohur area saw some of the heaviest loss of life on Thursday, with 20 civilians, eight of them children, killed there among 119 dead nationwide, the Observatory said.
The total death toll since the uprising against Assad's rule erupted in March last year now tops 26,000, the watchdog added.
Protesters demonstrated in Damascus, Daraa, Hama and also in Aleppo, chanting anti-regime slogans.
"We will not surrender, despite your tanks and guns!" they shouted in Assali, a Damascus district, while chants like "Treacherous soldier, shame on you!" echoed in Daraa as protesters accused regime troops of killing civilians.
-- 'Stop using heavy arms' --
The UN's Ban told Syrian Prime Minister Wael al-Halaqi and Foreign Minister Walid Muallem that the fighting must stop, "with the primary responsibility resting on the government to halt its use of heavy weapons."
Ban said at a news conference in Tehran broadcast live on Iranian television: "What is important at this time is that all the parties must stop the violence. All those actors who may be providing arms to both sides... must stop."
The International Committee of the Red Cross warned that the situation across large swathes of Syria was "edging towards irreversible deterioration."
"People fear for their lives every minute of the day," said Marianne Gasser, head of the ICRC in Syria.
A Turkish diplomat told AFP that Ankara would maintain its campaign for a safe haven inside Syria for the tens of thousands of civilians fleeing the violence after Davutoglu's appeal to the UN Security Council fell on deaf ears.
"We will continue to appeal to the international community to act," the diplomat said, speaking on condition of anonymity.
"This is not a situation that Turkey can handle on its own, but together with the international community."
Davutoglu on Thursday told the Security Council to act "without delay" to set up safe havens, warning that 80,000 Syrians are already in camps in Turkey, with 4,000 crossing the border each day.
Turkish officials say around 20,000 Syrians are also living in flats or hotels around the country.
"How long are we going to sit and watch while an entire generation is being wiped out by random bombardment and deliberate mass targeting?" Davutoglu asked, slamming the Security Council's failure to act.
But world powers failed to reach agreement on his proposal which would imply authorising a highly controversial protective military operation.
Britain's Foreign Secretary William Hague held a joint news conference with his French counterpart Laurent Fabius to warn that there are "considerable difficulties" with the idea of protected enclaves for civilians.
"We are excluding no option for the future. We do not know how this crisis will develop," Hague said. "It is steadily getting worse. We are ruling nothing out, we have contingency planning for a wide range of scenarios.
"But we also have to be clear that anything like a safe zone requires military intervention and that of course is something that has to be weighed very carefully."
Speaking to reporters after his speech, Davutoglu lashed out at the failure to agree a common line.
"A historic opportunity was missed," Davutoglu said in televised remarks. "Now is not the time to talk but to act. Turkey should not be expected to undertake the entire responsibility that the United Nations should take."
Syria's Deputy Foreign Minister Faisal Muqdad accused Turkey of facilitating the passage of "terrorists" into his country.
"Turkey nowadays trains and allows in terrorists, allows in Al-Qaeda. Most of the terrorists in Syria come from Turkey," he told Iran's Arabic-language Al-Alam television.
Turkish journalists, meanwhile, protested outside Damascus's embassy in Ankara to demand the release of two Turkish reporters reportedly being held by the Syrian regime.