At least 32 people, including eight civilians, were killed Sunday in airstrikes on the city of al-Raqqa, the Islamic State stronghold in Syria, a monitoring group reported.
The Syrian Observatory for Human Rights, which relies on a network of activists inside the war-torn country, said that the identity of the jets that mounted the strikes was not clear.
The bombardment struck civil facilities including a hospital, a playground and a school in al-Raqqa in north-eastern Syria.
The fatalities included 24 Islamic State militants, according to the Britain-based Observatory.
The air raids were the latest in a series in the area.
In recent months, a US-led military coalition and Russia have separately stepped up airstrikes on al-Raqqa with the aim of dislodging Islamic State from the city.
Sunday’s strikes come two weeks after Syrian regime forces, backed by Russia jets, retook the historic city of Palmyra from the al-Qaeda splinter group, who had controlled it for almost a year.
Palmyra's recapture, a significant military victory, boosted morale for the Syrian army, wearied by the country's multi-sided civil war that has entered its sixth year.
With support of allied Russia, the regime of Syrian President Bashar al-Assad looks eager to regain more ground from opposition forces.
Syrian Prime Minister Wael Nader al-Halki Sunday said that the Russian air force and Syria's military were crafting a joint operation that aims to free the northern city of Aleppo from rebel control.
"We, together with our Russian partners, are preparing an operation to liberate Aleppo and block all illegal armed groups that have not joined the ceasefire agreement or violated it," al-Halki told Russian lawmakers visiting Damascus, according to Russia's TASS state news agency.
Control of Aleppo is currently divided between a range of rebel groups and al-Assad's forces.
The rebels in northern Aleppo lost their front lines with al-Assad's forces in February, after they were cut off from Aleppo city due to intense Russian airstrikes backing the government.
Islamic State and al-Qaeda's Syria branch, al-Nusra Front, are excluded from a major US-Russian-brokered ceasefire in Syria, implemented in February and aimed at boosting indirect peace talks between the Syrian government and the opposition.
The Russian air force has been active in Syria since September, when Moscow launched a bombing campaign against insurgents there to support al-Assad, a long-time ally.
President Vladimir Putin announced a partial withdrawal of Russian troops from Syria last month, calling their task there "completely fulfilled."
However, Russian warplanes have since been instrumental in regime forces’ territorial advances in Syria.