Hayyan, a doctor and Homs resident whose parents remain in the al-Waer neighbuorhood, said the government launched 18 air strikes on Saturday, the last two of which dropped incendiary bombs.

Hayyan, who runs a volunteer group in the province, refused to be identified further due to concerns for his and his family's safety.

The British-based Syrian Observatory for Human Rights said a brother and sister were killed in the air strikes that left their bodies badly charred.

Al-Waer is the last rebel-held area in Homs, Syria's third largest city. It has been besieged for months with only intermittent international aid deliveries getting through.

The escalation against the neighbourhood comes after the evacuation of Daraya, a Damascus suburb, following a deal struck with the government after a gruelling bombing campaign and a tight siege.

Meanwhile Turkey's official news agency said a Turkish soldier has been killed and three others wounded in Syria.

The Anadolu Agency said two Turkish tanks in the Syrian town of Jarablus came under rocket attack by Kurdish militants.

The Turkish military began its so-called Euphrates Shield operation in Syria with Free Syrian Army units and coalition planes on Wednesday to push Islamic State militants out of Jarablus and to limit the advance of Kurdish forces to the west of the Euphrates River.

The soldier's death is the first reported fatality on the Turkish side.