Syrian rebels fired dozens of rockets at government forces in Aleppo and Latakia province on Friday, in preparation for a bid to break the siege of Aleppo city, a monitor said.
The rocket fire was accompanied by fierce clashes on the outskirts of the government-controlled west of Aleppo, with two suicide car bombings targeting a checkpoint in the Dahiyet al-Assad neighbourhood, the Syrian Observatory for Human Rights said.
"The rebels have begun a prelude to their operation to break the siege of Aleppo," Observatory director Rami Abdel Rahman said.
The Britain-based monitor also reported rebels had fired dozens of rockets at the Nairab military airport and Aleppo international airport, both east of Aleppo city and under government control.
And, simultaneously, rebels fired rockets from Idlib province into the government stronghold of Latakia, killing one person and wounding six.
The rocket fire hit near the Hmeimim military airport, which is used by government ally Russia, as well as near Qardaha, the ancestral village of President Bashar al-Assad, the monitor said.
Abdel Rahman said the operation involved a range of rebel groups, including the powerful Islamist Ahrar al-Sham and former Al-Qaeda affiliate Fateh al-Sham Front, previously known as Al-Nusra Front.
Ahrar al-Sham said on Twitter: "The prelude has begun with different types of weapons (targeting) the positions of the sectarian militias in Dahiyet al-Assad and surrounding areas in western Aleppo."
It also claimed the targeting of Nairab military airport with Grad rockets.
The Observatory said regime forces were returning rocket fire and also carrying out air strikes on the southern and western outskirts of Aleppo.
The city has been divided since mid-2012, and the eastern rebel-held neighbourhoods have been under regime siege near-continuously since July 17.
Rebels successfully broke the siege in early August, opening up a new route into the city from the south, but government forces quickly closed the route, and no aid has entered the east since July.
Damascus launched a Russian-backed assault on eastern Aleppo in late September that has killed hundreds of people and destroyed key infrastructure, including schools.
The assault and siege have prompted international condemnation, with UN aid chief Stephen O'Brien earlier this week describing Aleppo as a "kill zone."
Last week, Russia announced a unilateral "humanitarian pause" intended to allow civilians and surrendering rebels to leave, but only a handful of people left and the UN was unable to evacuate dozens of seriously wounded people.