The Syrian army has announced the start of a new military offensive in the rebel-held city of Aleppo.
State media quoted the army's military headquarters in Aleppo urging civilians in eastern parts of the city to avoid areas where "terrorists" were located and said it had prepared exit points for those who want to flee, including rebels.
The army's announcement did not say whether the campaign would also include a ground incursion.
Rebels said Russian and Syrian jets had escalated strikes in the past 24 hours on areas that control access to the city, whose rebel-held east has been besieged by Russian and Iranian-backed pro-government forces and completely encircled for all but a few weeks since July.
The Syrian Observatory for Human Rights also confirmed the intensification of raids on residential areas in eastern Aleppo, saying at least 14 people had been killed on Thursday, mostly civilians.
The United States and Russia have been leading diplomatic efforts to negotiate a lasting ceasefire and have been discussing how to coordinate attacks on militants from the Islamic State and the group formally known as the Nusra Front.
A seven-day-old ceasefire brokered by Washington and Moscow collapsed last week.
An AFP news agency journalist reported that his entire street in the Bustan al-Qasr district was left burning after warplanes dropped incendiary bombs. At least 13 people, including women and children, are believed to have died.
A deadly attack on an aid convoy and Syrian Arab Red Crescent warehouse outside Aleppo on Monday, for which Washington and Moscow have blamed each other, prompted the UN to temporarily suspend deliveries across the country.
But following the pause a convoy on Thursday entered Muadhamiya, a suburb of the capital, Damascus, where some 40,000 people are living under siege, the UN tweeted.
A spokesman hoped the UN could reach Aleppo "in the near future".
- BBC / Reuters