Turkish warplanes have bombed parts of north-eastern Syria at the start of an offensive which could lead to conflict with Kurdish-led allies of the US. Turkey's President Recep Tayyip Erdogan said the operation was to create a "safe zone" cleared of Kurdish militias which will also house Syrian refugees. The strikes have killed at least two civilians, Kurdish-led Syrian Democratic Forces (SDF) said. The group vowed to resist any Turkish advance across the border. It asked the US and the coalition against the jihadist group Islamic State (IS) to establish a no-fly zone in the area to stop "attacks on innocent people". The Kurds - key US allies in defeating IS in Syria - guard thousands of IS fighters and their relatives in prisons and camps in areas under their control and it is unclear whether they will continue to be safely detained. Turkish ground forces have been massing on the border. The offensive was launched just days after President Donald Trump controversially withdrew US troops from northern Syria, a decision announced after a phone call with Mr Erdogan that sparked widespread criticism at home and abroad. What is Turkey's plan?On Twitter, Mr Erdogan said the mission "was to prevent the creation of a terror corridor across our southern border, and to bring peace to the area" and that it would "preserve Syria's territorial integrity and liberate local communities from terrorists." The scale of the offensive was not yet clear, and there was no information on whether Turkish ground forces had attempted to enter Syria. Turkey plans to create a "safe zone" cleared of Kurdish militias - regarded by Ankara as terrorists - which will also house two million of Turkey's 3.6 million Syrian refugees.