Turkey has confirmed the strikes but said there is 'no joint operation' between Moscow and Ankara
Russian warplanes have for the first time bombed Islamic State targets around the Syrian town of al-Bab, which is surrounded by Turkish forces, allowing Turkish forces on the ground to advance further into the town.
The Dogan news agency, citing military sources, said the air strikes took place on Wednesday.
The report was published just after the announcement of a deal brokered by Turkey and Russia for a nationwide ceasefire in Syria, which will come into effect at midnight on Thursday local time.
Turkey's foreign minister, Mevlut Cavusoglu, on Thursday confirmed that the al-Bab strikes had taken place, but said there was "no joint operation" between Turkey and Russia over the advance on the town.
The Britain-based Syrian Observatory for Human Rights said "strikes suspected to be Russian" had been hitting al-Bab for the last two days "in support of the Turkish operation".
There has been no comment from the Russian army.
Turkey has for four months pressed an incursion against IS militants inside Syria in support of pro-Ankara fighters.
But they have faced stiffening resistance in the battle to take al-Bab, taking increasing casualties in the town some 30 kilometres south of the Turkey-Syria border.
Ankara had reportedly asked Washington to support its al-Bab campaign with air strikes earlier this week, but appears to have been refused.
Turkey has in recent days stepped up criticism of US-led anti-IS coalition forces for failing to back the Turkish incursion inside Syria with air support.
President Recep Tayyip Erdogan, who this week accused Washington of backing IS, on Thursday again attacked the US for its "support" for terror organisations in Syria.