After escalating threats over the past week, Turkish warplanes on Saturday began bombing the Kurdish-controlled enclave to back a ground attack by allied Syrian rebels.

More than a million people, including thousands of displaced families, live in towns and villages that dot Afrin's hilly terrain.

- Besieged enclave -

Afrin lies in a northwestern extension of Syria's Aleppo province, bordered by hostile Turkish forces to the west and north, and by pro-Ankara rebels to the south and east.

The region's only lifeline to the outside world is a single road to Syrian second city Aleppo, around 60 kilometres (40 miles) away.

"It's the sole outlet for the Afrin region, which is almost totally besieged," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, a British-based war monitor.

He said the road is open most of the time but pro-regime fighters from the Shiite towns of Nubul and Zahraa occasionally close it in protest.

The Kurdish-majority enclave includes around 360 different villages and towns, including the region's beating heart -- a town also called Afrin.

More than one million people call the area home, including displaced families from other parts of war-ravaged Syria.

- Guinea pig for self-rule -

When Syria's uprising erupted in 2011, ethnic Kurds across the country's north largely chose to remain on the sidelines, prompting criticism by the mainstream opposition for not facing off against regime troops.

The following year, Afrin became the first Kurdish area to fall out of government control and into the hands of the powerful Kurdish People's Protection Units (YPG) militia.

The militia, which has an estimated 5,000 fighters, strengthened their grip on the area, which stayed firmly outside opposition control.

That allowed the Kurds to use Afrin as a guinea pig for self-rule, a model they later implemented across areas they control in north and northeast Syria.

Pictures of Abdullah Ocalan -- the jailed leader of the affiliated Kurdistan Worker's Party (PKK) -- sprung up in Afrin.

Locals started speaking the Kurdish language, long banned by the Syrian government, and established schools, cultural centres and security forces.

As Kurds gained more ground across Syria's north, Afrin went on to become one of three administrative hubs, and one of the key cantons of a future Kurdish-run federal region.

The other two cantons are Syria's northeast Hasakeh province, dubbed "Jazira," and another called "Euphrates" that includes parts of Aleppo and Raqa provinces.

- Mountainous and agricultural -

Afrin is an agricultural area par excellence, with olive groves dotting its sloping hills.

Because of its rocky terrain, the region is known as Jabal al-Akrad, or the Mountain of the Kurds in Arabic.

The topography has allowed Kurdish fighters to reinforce their positions by digging trenches to fend off an attack by nearby rebels.

- Turkish threats -

On Saturday, Turkey launched a new air and ground operation to oust the YPG from Afrin, after days of escalating threats and military preparations.

Dubbing the new campaign operation "Olive Branch", the Turkish army said it was aimed against the YPG and also Islamic State (IS) jihadists.

Ankara considers the YPG a "terrorist" group because of its links to the outlawed PKK, which has waged a rebellion in the Turkish southeast for more than three decades.

Turkish President Recep Tayyip Erdogan fears the YPG's strength could inspire separatist notions within Turkey's Kurdish community and his army has bombed the group on several occasions since the start of Syria's war.

Erdogan has repeatedly vowed to uproot "nests of terror" in Syria, despite warnings that the operation could be militarily tough and complicate relations with Washington and Moscow.