Moscow/Beirut: Russia is sending more warplanes to Syria to further ramp up its campaign of air strikes, a Russian newspaper reported on Friday, as Moscow defied global censure over an escalation that Western countries say has torpedoed diplomacy.
In a statement issued by the White House after the two leaders spoke by telephone, US President Barack Obama and German Chancellor Angela Merkel described the Russian and Syrian bombing of Aleppo as "barbarous".
Fighting intensified a week into a new Russian-backed government offensive to capture all of Syria's largest city and crush the last remaining urban stronghold of the rebellion.
Moscow and its ally, Syrian President Bashar Al Assad, spurned a ceasefire this month to launch the offensive, potentially the biggest and most decisive battle in the Syrian civil war which is now in its sixth year.
Western countries accuse Russia of war crimes, saying it has deliberately targeted civilians, hospitals and aid deliveries in recent days to crush the will of 250,000 people trapped inside Aleppo's besieged rebel-held sector.
Moscow and Damascus say they have targeted only militants.
Hundreds of people have been killed in the bombing and many hundreds more wounded, with little access to treatment in hospitals that lack basic supplies.
Residents say the air strikes are unprecedented in their ferocity, deploying heavier bombs that flatten buildings on top of the people huddled inside.
Russia joined the war exactly a year ago.
The Kremlin said on Friday there was no time frame for Russia's military operation in Syria. The main result of Russian air strikes over the past year is "neither IS, nor Al Qaeda nor the Nusra Front are now sitting in Damascus", Kremlin spokesman Dmitry Peskov told reporters.
Britain's Special Representative to Syria, Gareth Bayley, said: "From Russia's first air strikes in Syria, it has hit civilian areas and increasingly used indiscriminate weapons, including cluster and incendiary munitions."
"Today, the reality in Syria is a nightmare. Aleppo is besieged again, with vital necessities such as water, fuel, and medicine running out for hundreds of thousands. Civilian infrastructure, including schools and hospitals, are being attacked."
The Izvestia newspaper reported that a group of Su-24 and Su-34 warplanes had arrived at Syria's Hmeymim base.
"If need be, the air force group will be (further) built up within two to three days," it quoted a military official as saying. "Su-25 ground attack fighters designated to be sent to Hmeymim have already been selected in their units and their crews are on stand-by, awaiting orders from their commanders."
The Su-25 is an armoured twin-engine jet which was battle-tested in the 1980s during the Soviet war in Afghanistan. It can be used to strafe targets on the ground, or as a bomber. Russia's defence ministry did not immediately respond to a request from Reuters for comment.
US Secretary of State John Kerry said on Thursday there was no point pursuing further negotiations with Russia over Syria. That leaves Washington - which is fighting IS militants in northern Syria but has avoided direct involvement in the war between Assad and his main opponents - with no backup plan for a policy that hinged on talks co-sponsored with Moscow.
After months of intensive diplomacy with Russia, conducted despite the scepticism of other senior Obama administration officials, Kerry reached agreement three weeks ago on a ceasefire. But it collapsed within a week, and Moscow and Damascus swiftly launched the latest escalation.
Western officials believe Moscow's decision to spurn the truce signals the Kremlin believes Assad's government can now win a decisive victory on the battlefield, after years of mostly stalemated war that killed hundreds of thousands of people and made half of Syrians homeless.
Syrian government forces and rebels fought battles on Friday in the city centre and north of Aleppo, where government troops had re-captured a camp for Palestinian refugees on Thursday that had already changed hands once since the start of the attack.
The sides gave conflicting accounts of the outcome of Friday's fighting. North of the city, the military said it had captured territory around the Kindi hospital near the refugee camp. Rebel sources denied the army had advanced there.
In the city centre, the military said it had advanced in the Suleiman Al Halabi district. Rebel officials said troops had moved forward but had subsequently been forced to withdraw.
A Syrian military source said government forces captured several buildings in the area and were "continuing to chase the remnants of the terrorists fleeing them". One of the rebel officials said government forces had "advanced and then retreated", losing "a number of dead".
The multi-sided Syrian civil war pits Assad against rebels.
The rebellion includes several groups inspired by or linked to Al Qaeda, and helped give rise to IS.
A Syrian rebel source familiar with the details of foreign military support said rebels had received promises of new arms, but so far there was nothing that would have an impact.
"If they don't give us anti-aircraft, they have no value," the source said.