More than 9,000 people, including nearly 4,000 civilians, have been killed in one year of Russian air raids in Syria, according to a monitoring group, as fierce fighting near the besieged city of Aleppo continues.

Russia launched an air campaign on September 30 last year in support of Syrian government forces, in a military intervention that has been widely credited with helping turn the balance of power in favour of President Bashar al-Assad.

Aleppo hospitals destroyed as Syria humanitarian crisis worsens

Since then, at least 9,364 people have been killed in Russian raids, according to the Britain-based Syrian Observatory for Human Rights, which uses a network of activists in Syria to track daily developments in the war.

The monitor said the death toll included about 3,800 civilians and 5,500 fighters from the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group and various rebel factions.

A further 20,000 civilians have been wounded in Russia’s year-long offensive of air strikes.

The observatory says it determines which planes carried out what raids according to their type, location, flight patterns and the munitions involved.

Observatory director Rami Abdel Rahman said the death toll from Russian strikes could be even higher given the number of people killed by unidentified fighter jets.

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Later on Friday, the Russian government rejected the figures provided by the Observatory.

"We do not consider information about what happens in Syria from an organization based in Britain to be reliable," Kremlin spokesman Dmitry Peskov told reporters.

Peskov also said there is no timeframe for Russia's military operation in Syria, adding that the main result of Russian air strikes over the past year is that "neither Islamic State [ISIL], nor al-Qaeda nor the Nusra Front [currently known as Jabhat Fateh al-Sham] are now sitting in Damascus".

Upon launching its air campaign in Syria, Russia had said its aerial campaign targeted ISIL and other "terrorists", but rebel forces and their backers accused Moscow of focusing on moderate fighters instead.

Several medical groups also accused Russia of strikes that had hit field clinics and hospitals in Syria.

A US-led coalition air campaign has also been accused of straying from its stated mission to fight ISIL. One air raid killed dozens of Syrian soldiers earlier this month.

'Merciless abyss'

The one-year anniversary of Russia’s military intervention came a day after Moscow said it would press on with its bombing campaign in Syria, ignoring a threat by Washington to suspend its engagement over the conflict following escalating attacks on rebel-held parts of Aleppo.

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Syrian and Russian aircraft have carried out a series of intense bombing raids on east Aleppo since Assad’s government announced an offensive last week to retake all of the divided city following the failure of a short-lived ceasefire brokered by Russia and the United States.

Moscow and Washington have traded blame for the collapse of the truce, with US Secretary of State John Kerry admitting on Thursday that months of diplomacy to end the war had hit a dead-end.

"I think we are on the verge of suspending the discussion because, you know, it's irrational in the context of the kind of bombing taking place, to be sitting there, trying to take things seriously," Kerry said.

The  joint bombardment of Aleppo has been some of the worst in Syria's long-running civil war, killing about 400 people and wounded 1,700 others.

An estimated 250,000 people still live in eastern Aleppo, which has been under near-continuous siege since mid-July, causing food and fuel shortages.

"The statistics are pretty horrific," said Al Jazeera’s Charles Stratford, reporting from Gaziantep on the Turkish side of the Turkey-Syria border, citing UN officials who called for the urgent evacuation of at least 600 wounded people in Aleppo.

According to UN aid chief Stephen O'Brien, Aleppo is descending into a "merciless abyss of a humanitarian catastrophe unlike any we have witnessed so far in Syria".

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"The situation remains absolutely desperate in that part of the city, and what seems to be fuelling the fear now among civilians in that area is what's been reported as a gradual build-up of what’s been described as pro-Syrian government and government forces pushing forward and closer to the outskirts of that area," Al Jazeera's Stratford said.

On Friday, opposition activists said Syrian government helicopters had dropped at least two barrel bombs on Aleppo's Old City, while one person was reportedly killed in an artillery strike in the eastern part of the city, Stratford said.

Two of the biggest hospitals in the city's east were bombed on Wednesday in what UN Secretary-General Ban Ki-moon described as a war crime.

Children attend underground school in Syria’s Aleppo

UK-based charity Save the Children also warned said the "ferocious assault" on the city could deprive almost 100,000 school-age children of an education.

READ MORE: 'Most of Aleppo's public schools are destroyed'

Aleppo was once Syria's commercial and industrial heart but has been ravaged by fighting and roughly divided between government control in the west and rebel control in the east since mid-2012.

The Syrian civil war started as a largely unarmed uprising against Assad in March 2011, but quickly escalated into a full-blown armed conflict.

Five years on, more than 400,000 Syrians are estimated to have been killed, and almost 11 million Syrians - half the country's prewar population - have been forced to flee their homes.

Source: Al Jazeera News And News Agencies