The UN secretary-general says the sputtering peace talks are at a critical juncture after a convoy was bombed, killing 20. German Vice Chancellor Sigmar Gabriel slammed the attack, calling it a huge setback for peace.
The bombing of the besieged city of Aleppo intensified during the overnight hours and continued into the day amid a desperate attempt to salvage a failed ceasefire.
UN Secretary-General Ban Ki-moon said the Syrian peace process was at a "make or break moment," as US and Russian diplomats were due to meet with other key players in New York later on Thursday.
The ceasefire agreement negotiated between Washington and Moscow collapsed earlier this week, unleashing a new round of fighting in a 5-year-old civil war that has been marked by brutality.
Devastating air strikes set off large-scale fires across much of rebel-held sections of Aleppo, while heavy fighting consumed fringe areas of the city.
A correspondent for the French news agency AFP in eastern Aleppo said his entire street was in flames following massive pre-dawn airstrikes.
Activists at the Aleppo Media Center said the fires were sparked by "incendiary phosphorous bombs." Volunteer firefighters were left to battle the blazes throughout the night.
Online footage of the bombings, posted by the group, showed a ball of fire lighting up the skyline and sparking fires across the city.
Intense bombing assault
The Syrian Observatory for Human Rights counted 14 strikes on the rebel-held neighborhoods of Bustan al-Qasr and Al-Kalasseh, which "led to massive fires" overnight.
Observatory head Rami Abdel Rahman called them "the most intense strikes in months" on those two districts. He put the death toll at seven, including three women and three children.
"The nonstop strikes last night were so violent I can't even describe them," said Ibrahim Abu al-Leith, spokesman for a prominent Syrian group of emergency responders known as the White Helmets.
Meanwhile, the jury for the Swedish human rights award known as the "alternative Nobel prize" announced on Thursday that the White Helmets won the Right Livelihood Award "for their outstanding bravery, compassion and humanitarian engagement."
Renewed airstrikes also pounded Aleppo's Sukkari neighborhood, which coincided with fierce clashes in the southwestern district of Ramussa, where rebel groups are battling a government offensive, according to the Observatory.
Despite the violence, the UN has resumed aid deliveries – their first operation since a deadly strike on an aid convoy a few days ago.
"Today we are sending an inter-agency, cross-line convoy with urgently needed aid to people in a besieged area of rural Damascus," UN humanitarian agency (OCHA) spokesman Jens Laerke said.
The attack on the aid convoy has been widely condemned. In Moscow on Thursday, German Vice Chancellor Sigmar Gabriel pressed the Kremlin to carry out a thorough investigation of the attack, which killed at least 20 civilians.
Gabriel deplored the attack as a "dramatic setback" for the peace process in Syria. "We are not able," he said, "to resolve this conflict without Russia."
bik/jil (AFP, dpa)