Rebels said they shot down a MiG warplane on Thursday as violence whipped across Syria ahead of a UN Security Council meeting on deteriorating humanitarian conditions in the country and along its borders.

Egyptian President Mohamed Morsi, meanwhile, caused a storm with a speech at a Non-Aligned Movement summit in Tehran, slamming the Damascus regime as "oppressive" and urging support for the opposition.

"A MiG was shot down this morning by our men using automatic weapons, shortly after taking off from Abu Zohur military airport in Idlib province," the rebel Free Syrian Army chief for the northern province, Colonel Afif Mahmoud Suleiman, told AFP.

The Britain-based Syrian Observatory for Human Rights said regime forces retaliated by shelling the area, and that eight children and nine women were among at least 20 people killed.

The opposition Syrian National Council, meanwhile, renewed its call for the Security Council to impose no-fly zones.

Accusing the government of "crimes" and "barbaric acts," the SNC said a no-fly zone and corridors were essential to protect almost 2.5 million civilians displaced by the conflict or who fled across the borders with Syria's neighbours.

On August 13, rebels claimed they downed a Russian-made MiG in the eastern province of Deir Ezzor, and on Monday rebels said they had shot down a helicopter during fierce fighting in the Damascus suburb of Qaboon.

The Syrian regime acknowledged the first two aircraft crashes but put them down to mechanical failures. It made no immediate comment on the latest claim.

The Syrian Observatory had earlier said rebels took over parts of a military airport in Idlib overnight, and that explosions could be heard from inside the facility.

The violence came as a war of words erupted between Egypt's Morsi and Syrian Foreign Minister Walid Muallem in the presence of NAM leaders after their summit began in Iran's capital.

"Our solidarity with the struggle of Syrians against an oppressive regime that has lost its legitimacy is an ethical duty, and a political and strategic necessity," the Egyptian leader said.

With his delegation walking out in protest, Muallem accused Morsi of using his speech to incite further bloodshed in Syria.

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The speech amounted to "interference in Syria's internal affairs and... incites continued bloodshed in Syria," he said, quoted from Tehran on Syrian state television.

On the sidelines of the summit, Morsi held talks with Iranian President Mahmoud Ahmadinejad on bilateral and regional issues including Syria, an official said.

"They emphasised the need to solve the Syria crisis via diplomacy and to prevent foreign intervention," Iranian Deputy Foreign Minister Hossein Amir Abdollahian told Iran's Arabic-language broadcaster Al-Alam.

Thursday's UN Security Council meeting was called by France and aimed at "appealing to world conscience and for mobilisation" in the face of the Syrian humanitarian drama, a diplomat said in New York.

Turkey has floated the idea of creating buffer zones within Syria to receive those displaced by the conflict so they do not flood across the borders into neighbouring countries.

Assad, however, dismissed the idea in an interview on Wednesday with the pro-regime Addounia TV channel.

"Talk of buffer zones firstly is not on the table and secondly it is an unrealistic idea by hostile countries and the enemies of Syria," the embattled leader said.

Ahead of the Council meeting, British Foreign Secretary William Hague played down expectations. "We are excluding no options for the future," he said, adding however there were "considerable difficulties with such an idea."

Along with France, Britain announced new humanitarian aid for Syria. London is to give an extra three million pounds (4.75 million dollars) and France five million euros (6.2 million dollars), their foreign ministers said in New York.

Syria's neighbours Jordan, Lebanon, Turkey and Iraq were all to send ministers to the meeting.

On the warfront, fierce clashes broke out near a military security headquarters in Deir Ezzor city of east Syria, while in the northern city of Aleppo, the Salaheddin, Saif al-Dawla and Sukari districts saw renewed fighting, the Observatory said.

In Damascus, gunfire reverberated across Qaboon and fighting also erupted in the southern area of Tadamun, according to activist groups.

The Britain-based Observatory reported a total of at least 77 people killed in violence across the country on Thursday, including 46 civilians, four of whom died in the city of Aleppo.

The director of the capital's Tishrin military hospital, meanwhile, said more than 8,000 members of the security forces have been killed since the uprising against Assad's rule broke out in March 2011.

"I estimate that at least 8,000 soldiers and members of the security forces have been killed since the beginning of the crisis," the director told AFP.

The Observatory, which says more than 25,000 people have been killed in the 17-month-old uprising, puts the figure of soldiers and members of the security forces killed at nearly 6,500.

Activists called for the usual Friday protests to be held this week under the banner of "Daraya, a flame which will not go out," after a massacre of hundreds of people in the town near Damascus last week that each side blamed on the other.

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