Shells and airstrikes rained down on opposition-held parts of Aleppo Thursday, despite a temporary ceasefire designed to allow humanitarian aid into the contested Syrian city, activists said.
Unidentified warplanes mounted dozens of strikes on rebel-held districts in south-western Aleppo, which has effectively been a divided city since mid-2012, the Syrian Observatory for Human Rights reported.
Clashes were also under way between rebels and regime forces in the area, said the Britain-based Observatory, which relies on a network of activists inside Syria for its information.
At least five rebels were killed, the watchdog said. It did not report casualties among regime forces.
On Wednesday, Russia, a key ally of Syrian President Bashar al-Assad, said all military hostilities in Aleppo would halt for three hours a day for three consecutive days starting Thursday to allow humanitarian convoys to deliver aid to civilians there.
The ceasefire had been due to begin at 10 am local time (0700 GMT).
Brita Hagi Hassan, the head of the Aleppo Local Council on the rebel side, dismissed Russia's truce announcement as "mere media propaganda."
"Their planes have not left the Aleppo skies," Hassan told dpa in a Facebook message.
Meanwhile, activists inside Aleppo reported that regime helicopters dropped barrels allegedly containing chlorine gas on the city's opposition-held district of Zabadieh late Wednesday, killing a woman and her child.
Activist Mahmoud al-Shami, based in the rebel side of Aleppo, posted pictures on his Facebook page showing a father and his 1-year-old baby being treated for breathing problems allegedly caused by chlorine inhalation.
The claims could not be independently verified.
Chlorine gas can cause breathing problems and foaming blood from the mouth.
French Foreign Minister Jean-Marc Ayrault expressed concern about the alleged chlorine attack.
"I strongly condemn all attacks on the civilian population, all the more when chemical weapons are used," Ayrault said in a statement.
The Syrian government and rebels have been repeatedly accused of using banned chemical agents in the conflict, now in its sixth year.
There has been a spike in attacks on medical facilities in Syria in recent months, Human Rights Watch said on Thursday.
"Airstrikes on hospitals are becoming routine in Syria, but we have yet to see any investigation or accountability for these criminal acts," said Nadim Houry, the watchdog's deputy Middle East director, said.
"With heavy bombing continuing relentlessly in Aleppo especially, hospitals and clinics need to be treated as the sacred life-saving places they are, not as additional bombing targets," he added.
The Islamic state extremist militia has taken advantage of Syria's strife to establish a foothold in the country.
The al-Qaeda splinter group has suffered military setbacks and lost ground in Syria since September, when Russia started an air campaign in the country in support of al-Assad.
At least 30 people, including 24 civilians, were killed Thursday in airstrikes by Russian jets targeting al-Raqqa, the Islamic State's de facto capital in Syria, the Observatory said.
The synchronized strikes also left 70 injured and an unspecified number of missing people in the north-eastern city.
"Today's air raids in al-Raqqa were the fiercest in about three months," Mohammed Ibrahim, a doctor in a local hospital, said.
He added at least 16 raids were carried out by Russian aircraft against civil sites in the city.
"There are no longer obvious positions for Daesh in al-Raqqa," Ibrahim told dpa, using an Arabic acronym for Islamic State.
In Moscow, the Russian Defence Ministry said its long-range Tupolev-22M3 bombers had hit a number of Islamic State targets, including a chemical ammunition plant near al-Raqqa.
"Six long-range Tupolev-22M3 bombers took off from a base in Russia to deal a pinpoint strike with high-explosive fragmentation bombs against facilities of the terrorist group called Islamic State in the south-east, north and north-west of Raqqa," the Defense Ministry added, according to state news agency TASS.
On Monday, Russian bombers attacked Islamic State's facilities near Palmyra in central Syria.