Bombardment of the northern city of Aleppo shows no sign of ending even as the Syrian military extends a unilateral ceasefire around Damascus and opposition strongholds nearby for another 48 hours.
Monday's announcement of the truce extension came as a humanitarian convoy delivered aid to 12,000 families trapped in a government-besieged area in central Syria.
The Aleppo fighting threatens to scuttle the first peace talks in Geneva between President Bashar al-Assad's representatives and opposition groups which are due to resume at an unspecified date after breaking up in April.
Between 350,000 and 400,000 people are believed to remain in rebel-held parts of Aleppo, once a city of two million.
Meanwhile, in Geneva, John Kerry, the US secretary of state, said "several proposals", aimed at finding a way to restore at least a partial truce in Syria, were being discussed.
"We're getting closer to a place of understanding, but we have some work to do, and that's why we're here," he said at the start of a meeting on Monday with Adel al-Jubeir, Saudi Arabia's foreign minister.
After meeting Jubeir and Staffan de Mistura, the UN envoy for Syria, Kerry said he hoped for more clarity in the next day or so on restoring the nationwide ceasefire.
"What is happening in Aleppo is an outrage. It's a violation of all humanitarian laws. It's a crime," Jubeir said.
"It's a violation of all the understandings that were reached."
De Mistura, for his part, said he would travel to Moscow for talks.
The US and Russia had agreed to keep extra staff in Geneva to work on the ceasefire.
"Both sides, the opposition and the regime, have contributed to this chaos, and we are working intensely in order to try to restore the cessation of hostilities," Kerry said.
The peace talks in April in Geneva failed to make any headway, but De Mistura has said he hopes they can resume "during the course of May".
On Monday, France also called for a ministerial meeting of the international group supporting Syria to "restore the ceasefire".
Russian role in question
Al Jazeera's Diplomatic Editor James Bays, reporting from Geneva, said both opposition delegates and diplomats were questioning Russia's role in the peace efforts.
"Many diplomats will tell you Russia is not properly invested in this political process, that instead it seems they are pursuing or allowing their allies to pursue a military option," he said.
"The process is very close to collapse ... if they cannot get the cessation of hostilities back in place."
The government declared its ceasefire on Friday around Damascus, the capital's Eastern Ghouta suburbs and the coastal Latakia region in the wake of two weeks of rising violence.
Russia's Tass news agency quoted Lieutenant-General Sergei Kuralenko, head of the Russian coordination centre in Syria, as saying that the Damascus area ceasefire was brokered by Russia and the US "in agreement with the Syrian leadership and the moderate opposition".
But more than three dozen rebel factions said on Saturday they would not respect the truce unless the government agreed to extend it over the whole country.
The latest partial truce in Syria does not cover Aleppo, the country's largest city and the scene of its worst violence in recent weeks.
Russian and American officials said they were working to arrange a truce for Aleppo.
Rebels and government forces are battling each other with rockets and bombs across Aleppo and its outskirts.
'Barrel bombs' dropped
Rebels on Monday lobbed rockets into government-held areas in the western part of Aleppo while government helicopters dropped "barrel bombs" - crude and unguided explosives - on opposition-held areas in the city and surrounding villages, according to the Britain-based Syrian Observatory for Human Rights (SOHR).
Separately, a car bomb detonated in the rebel-held Salhin neighbourhood of Aleppo, appearing to target an Islamic judiciary council.
The explosion wounded a lawyer and several other people, according to the Local Coordination Committees, an activist network.
The Syrian Civil Defence, also known as the White Helmets, which organises rescue operations in opposition-held areas of Aleppo, said several civilians were killed and wounded, including a judge for the Ahrar al-Sham rebel group.
Fierce violence has taken the lives of more than 250 civilians over the previous nine days, according to the SOHR, while only six died in violence on Sunday.
Syrian state television said on Monday that a missile hit the surroundings of Aleppo University Medical Hospital, and several civilians were injured by rebel mortar attacks on the residential area of Jamiyat Hay al-Zahra in western Aleppo.
The rebel-held local council of Aleppo city announced a state of emergency in areas it runs due to the intense bombardment.
The opposition accuses the Assad government of deliberately targeting civilians in rebel-held parts of Aleppo to drive them out.
For its part, the government says rebels have been heavily shelling government-held areas, proving that they are receiving more sophisticated weaponry from their foreign supporters.
The ISIL dimension
In the countryside north of Aleppo, other rebel groups have been fighting against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group, which is not party to any ceasefire.
Amaq, a news agency affiliated to ISIL, said the group's fighters had gained control of the villages of Doudayan, Tel Shaer and Iykda from rival rebels in the northern Aleppo area near the border with Turkey.
They said that they were able to cut the supply routes of other rebels in the area, despite Turkish artillery shelling to aid the rebels against ISIL.
SOHR said the ISIL fighters staged a counterattack to regain lost ground but there had been no major gains for any side.
|The latest partial ceasefire in Syria does not cover Aleppo, the country's largest city and former commercial centre [Reuters]
On the humanitarian front, the news was more encouraging.
Relief efforts by the International Committee for the Red Cross continued, with a convoy of 13 Red Cross lorries and three trucks from the Syrian Arab Red Crescent delivering food, hygiene items, diapers and school books to the besieged town of Talbiseh, north of the central city of Homs, Pawel Krzysiek, a Red Cross spokesman, said on Monday.
The population of Talbiseh has doubled to 60,000 with the influx of displaced residents from other areas, according to the Red Cross.
Syria's conflict erupted in 2011 after the repression of anti-government protests and has since escalated into a complex, multi-faceted war, which has killed more than 270,000 people.
Source: Al Jazeera and agencies