Beirut: Dozens of people were killed in an intense day-long battle between Syrian rebels and government forces in western Aleppo that continued intermittently on Wednesday, with rebels saying they were forced to retreat by heavy aerial bombing.
An insurgent assault in and around the Jamiyat Al Zahraa area of Aleppo had threatened the army's defensive lines around government-held districts of a city at the epicentre of a recent escalation in the five-year-old civil war.
The surge in bloodshed in Aleppo, Syria's largest city and biggest strategic prize, wrecked the first major "cessation of hostilities" agreement of the war, sponsored by Washington and Moscow, which had held since February.
The German and French foreign ministers said that achieving a ceasefire in Aleppo was critical to renewing peace talks.
"I believe everyone knows and can conclude that there could be no return to the political talks in Geneva if a ceasefire in and around Aleppo is not observed," German Foreign Minister Frank-Walter Steinmeier told reporters in Berlin.
Meanwhile, late in evening, the US State Department said the United States and Russia have agreed to extend a cessation of hostilities in Syria to include Aleppo province and will coordinate to strengthen monitoring of the new arrangement.
It is critical that Russia redoubles efforts to press Syrian President Bashar Al Assad to comply with the new arrangement while Washington does its part with Syrian opposition forces, the department said in a statement.
"Our objective remains, and has always been, a single nationwide cessation of hostilities covering all of Syria - not a series of local truces," the statement said.
In Geneva, a senior United Nations humanitarian official said the Syrian government was refusing UN demands to deliver aid to hundreds of thousands of civilians trapped by the fighting, including many in devastated Aleppo.
The Syrian Observatory for Human Rights said dozens had been killed on both sides in what it described as the most intense battle in the Aleppo region in a year. Government forces were reinforced by allies, it said.
A rebel fighter said about 40 government soldiers had been killed, while rebel losses stood at 10 dead. A military source denied there had been heavy casualties in army ranks, but said dozens of civilians and many rebels had been killed.
Rebel sources said insurgents had at one point captured a strategic location known as Family House, but later lost it after the government side sent in reinforcements.
A pro-government military strategist said the offensive failed to breach key army defence and supply lines in Aleppo.
"The assault was repelled, foiling a major attempt by these terrorist groups to make a breakthrough into the heart of Aleppo," Hassan Hassan said on state-run Ikhbariyah TV.
A rebel source said sustained air strikes on insurgents arrayed along the fringes of government-controlled Jamiyat Al Zahraa had forced them into a retreat.
"The air force is the only weapon that exhausts us, especially (the use of) barrel bombing," said Mohammad Al Sulaiman, a field commander from the Free Syrian Army's Liwa Fursan Al Haq brigade.
Rebels said jets believed to be both Russian and Syrian continued to pound their positions near Jamiyat Al Zahraa. Other air and artillery strikes hit rebel emplacements around the Castello highway, the main supply route into rebel-held Aleppo.
Most of the people killed in Aleppo in the last few weeks have been civilians. The Observatory said 279 civilians had been killed in Aleppo by bombardment since April 22 - 155 of them in opposition-held areas and 124 in government-held districts.
Syria's conflict has killed at least 250,000 people and displaced half its pre-war 22 million population, giving rise to the world's worst refugee crisis.
Russia turned the tide of the war in Syrian President Assad's favour with a campaign of heavy aerial bombing launched last September, while the United States and some allies have provided limited support to rebel forces.
Temporary local ceasefires have been put in place in two areas of Syria but those have not been extended to Aleppo.
Syrian opposition figure Riad Hijab, speaking before talks with the German and French foreign ministers and the UN's Syria envoy, said a general ceasefire was needed across Syria, rather than one confined to specific regions.
That formula is not working, said Hijab, adding that the opposition had reached a dead end with Assad in peace talks.
"There needs to be an agreement according to UN Security Council Resolution 2268 that includes all Syrian areas where moderate opposition exists," he said.
On Wednesday, Russia blamed the United States and an upsurge in violence by Nusra Front militants for a failure to extend a ceasefire plan to Aleppo the previous day.
Russian Foreign Minister Sergei Lavrov said on Tuesday that the deal covering Aleppo was close and that the Russian and US militaries might announce a decision "in the coming hours". But such a local truce, also known as "a regime of calm," never materialised.
Russian news agencies quoted Defence Ministry spokesman Igor Konashenkov as saying Russian and US military officers were holding "active consultations" with the Assad government and "moderate opposition" on how to salvage the truce plan.