BEIRUT: Syrian warplanes stepped up airstrikes on rebel-held districts in Aleppo on Tuesday, the third day of an assault that has killed more than 100 people in the northern city, activists said.
The strikes come hours after U.N. Secretary General Ban Ki-moon demanded a cease-fire in the nearly 3-year-old conflict, in which more than 120,000 people have been killed.
The escalation suggested the Assad government was redoubling efforts to drive the opposition out of Aleppo, Syria's largest city and once the country's commercial hub, before a peace conference expected to take place in Switzerland in five weeks.
The opposition has controlled parts of the city for more than a year. On Tuesday, the main Western-backed opposition group, the Syrian National Council, accused the international community of "failing to take any serious position that would guarantee a stop to the bloodbath" ahead of the talks.
The Britain-based Syrian Observatory for Human Rights said Tuesday that the airstrikes had killed 15 people, including two children, in the rebel-held Shaar district.
On Sunday, 76 people, including 28 children, died in air raids, opposition groups said. The city was hit by another round of airstrikes on Monday.
Ban told reporters in New York on Monday that the situation in Syria has "deteriorated beyond all imagination" and insisted that the fighting stop before political dialogue on Syria can start.
Brokered by Russia and the United States, peace talks between the Syrian opposition and Assad's government are scheduled to begin in January in the Swiss city of Montreux.
Plans are under way to organize a one-day meeting of foreign ministers in the city ahead of the Syrian talks, U.N. officials said Tuesday.
U.S. Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and more than two dozen other foreign ministers would gather for the Jan. 22 meeting at a Montreux hotel.
The conference will later reconvene on Jan. 24 for the start of actual negotiations between Syria's warring sides, said Khawla Mattar, a spokeswoman for the U.N.'s special envoy to Syria, Lakhdar Brahimi.
Violence in Syria has surged in the past weeks as the warring sides try to claim or hold on to territory as a possible bargaining chip in the negotiations.
The U.N. chief on Monday called for a cease-fire ahead of the peace conference, to give a chance for it to succeed, but the call fell on deaf ears.
Civilians continue to pay the highest price in the conflict after even the most modest attempts at peace have failed.
On Monday alone, at least 150 people were killed nation-wide, according to the Observatory, which relies on a wide network of activists on the ground. Most of the casualties were reported in and around Syria's largest cities, including in the capital, Damascus, Aleppo and the central city of Homs.
The high daily death toll coincided with the United Nations' $6.5 billion appeal to help displaced Syrians and their host countries as civil war is expected to rage on well into 2014.
Nearly 9 million Syrians have been uprooted from their homes, with some 2.3 million fleeing into neighboring countries and millions of other searching for shelter in safer parts of Syria.