Rebels in Syria have announced a big offensive aimed at breaking the government siege of east Aleppo.
A UK-based monitoring group said the rebels had fired “hundreds” of missiles into western Aleppo, killing at least 15 civilians.
They are also reported to have targeted al-Nayrab military airport to the east.
About 275,000 people have been besieged in the east by pro-government forces for several months.
The Syrian government said it had repelled offensives on several fronts around Aleppo by both rebel groups and militants from so-called Islamic State (IS).
“Booby-trapped cars, two tanks and a large number of armoured vehicles” were destroyed, the defence ministry said on its website.
Syria and its ally Russia have recently intensified air strikes on the east.
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Russia said it was time for all rebel groups in eastern Aleppo to be considered “legitimate targets”.
The attacks are so far coming from rebels outside Aleppo but it is understood that rebels inside the city will join the offensive.
“All the revolutionary factions, without exception, are participating in the battle,” the military spokesman for the Fastaqim faction inside the city said, AP news agency reports.
They include Jabhat Fateh al-Sham, formerly the al-Qaeda-linked Nusra Front, as well as fellow Islamists Ahrar al-Sham.
Rebels fired Grad missiles at al-Nayrab, the Syrian Observatory for Human Rights (SOHR) monitoring group said. Up to 115 people were killed or wounded, it added.
They also detonated two car bombs against government positions to the south-west of the city. One was a tank driven by a French suicide bomber from Jabhat Fateh al-Sham, a spokesman for the group said.
The area around the Hmeimim air base near the coastal city of Latakia – the main airport used by the Russian air force – was also reportedly targeted, the SOHR said.
Analysis – James Longman, BBC News, Beirut
The rebels said this counter-attack would come. But even though disparate groups have united for this effort, “liberating” East Aleppo won’t be easy.
They have hit an airbase and are targeting other Syrian positions in an effort to cripple any response.
But the Syrian army is the least of their problems – by itself, it is relatively weak. The Syrian government is supported by Lebanese, Iranian, Iraqi and Afghan Shia militias, as well as Russian air power – soon to be bolstered by a naval fleet in the Mediterranean.
One of the main rebel factions spearheading this operation is Jabhat Fatah al-Sham, which is affiliated to al-Qaeda. It is the very group the US has tried to untangle from the fighters it supports.
This means that from a Western perspective at least, the rebels are on their own.
The rebel offensive came as Syria’s foreign minister Walid Muallem met his Russian and Iranian counterparts, Sergei Lavrov and Mohammad Javad Zarif, in Moscow. They pledged to increase support for the Syrian government.
Mr Lavrov reiterated Moscow’s call for moderate rebel groups to disassociate themselves from Jabhat Fateh al-Sham.
He quoted US Secretary of State John Kerry as saying if this did not happen the moderate groups concerned would be considered a legitimate target.
“I think… the time has come for the logic set out by John Kerry to find some practical shape,” he said.
Mr Lavrov also accused US-backed rebels in Syria of impeding humanitarian operations in Aleppo, adding that UN humanitarian workers had behaved “unprofessionally” by failing to allow sick and injured civilians out of the city.
Mr Muallem accused the West of attempting to drive IS militants from Iraq to Syria to fight the Syrian government.
It is the rebels’ second attempt to break the siege. In August they temporarily opened a corridor between the east and west after the government entirely encircled them for the first time in July.
The city, previously Syria’s economic hub, has been divided between the two sides since 2012.
Almost 500 people have been killed and 2,000 injured since government forces, backed by Russian air strikes, intensified an assault on the east of the city a month ago.
UN human rights chief Zeid Raad Al Hussein has described the city as a “slaughterhouse”.