Syrian government aircraft have bombed besieged rebel-held eastern districts of the city of Aleppo for the first time in three weeks, activists say.
The Syrian Observatory for Human Rights reported that at least five people were killed as a number of areas were hit.
The government and its ally Russia halted air strikes in mid-October to allow civilians and rebels to leave.
Russia denied it had resumed attacks on Aleppo, but said it had launched missiles at jihadist groups elsewhere.
Russia's only aircraft carrier, the Admiral Kuznetsov, was also used in combat for the first time, with Su-33 fighters flying sorties from the eastern Mediterranean.
But footage of the aircraft from Russian media outlets show them equipped with air-to-air missiles rather than bombs.
Government forces launched a major assault on rebel-held eastern Aleppo on 22 September, two weeks after placing it under siege.
Since then, troops have pushed into several outlying areas with the help of Iranian-backed Shia militias and Russian air strikes.
Rebels launched a counter-attack in an attempt to break the siege in late October. But their progress slowed after early gains.
The UN says weeks of air strikes and shelling have killed more than 700 civilians in the east, while rocket-fire has left scores dead in the government-controlled west.
On Tuesday, activists said the three-week moratorium on air strikes declared by Russia had seemingly ended.
Warplanes and helicopters reportedly bombed the Haidaria, Masakin Hanano, Sakhour, Sheikh Faris, Bab al-Nairab, Qadi Askar and Qaterji districts.
"Our houses are shaking from the pressure. Planes are soaring above us and the bombardment is around us," resident Modar Shekho told the Reuters news agency.
Russian Defence Minister Sergei Shoigu did not mention Aleppo when he briefed President Vladimir Putin on Tuesday about the start of a "major operation" against so-called Islamic State and Jabhat Fateh al-Sham, which was known as al-Nusra Front until it formally broke off ties with al-Qaeda in July.
Mr Shoigu said a frigate, the Admiral Grigorovich, had fired Kalibr cruise missiles at targets in Idlib and Homs provinces. The Su-33s on board the Admiral Kuznetsov and the Bastion mobile coastal defence missile system were also involved.
The targets included "terrorist" training centres, arms depots, as well as "factories producing various weapons with fairly serious mass destruction capacity".
The Local Co-ordination Committees, an opposition activist network, reported that a missile hit the town of Saraqeb in Idlib province, and that Russian warplanes had targeted the towns of Ariha, Ihsim, Khan Sheikhoun and Tal Nabi Ayoub.
The LCC also said there had been air strikes on several locations in Aleppo province on Tuesday, including one that damaged a hospital in Awaijel. At least one person was killed in the attack, the third on a medical facility in 24 hours, it added.