Turkey targets Kurdish forces in Afrin: The short, medium and long story

Turkey says it is getting ready to launch a massive assault on Kurdish forces on the other side of the border with Syria - potentially putting it in direct conflict with its Nato ally, the United States.

This could be a significant new development in the Syrian civil war, which is now almost seven years old. We've boiled down why it matters.

You can choose to read the short, medium or long story below, either by themselves or one after the other.

The Story in 100 words :

Why is Turkey threatening this assault?

One main reason: Turkey considers the US-backed Kurdish militia that controls much of north-eastern Syria a terrorist group.

Turkey says the militia is an extension of a Kurdish rebel group it has fought for decades, and wants to prevent it consolidating its hold on Syrian territory.

Recent news of US plans to help the militia form a 30,000-strong "border security force" alarmed Ankara.

Turkey's president said Washington was "creating a terror army" and vowed to "suffocate" it.

He warned of imminent operations to clear Kurdish forces from two border areas - Afrin and Manbij.

The Story in 300 words :

Turkey has vowed to crush a Syrian Kurdish militia called the People's Protection Units (YPG), which it considers a terrorist group.

Turkish President Recep Tayyip Erdogan says it is an extension of the banned Kurdistan Workers' Party, which has fought for Kurdish autonomy in Turkey for three decades.

The YPG denies any direct links - an assertion backed by a US-led coalition whose air strikes have helped the militia and allied Arab fighters drive Islamic State militants from tens of thousands of square kilometres of Syria.

Ankara has condemned the US for supporting the YPG and was alarmed when it emerged on Saturday that the coalition was helping it form a 30,000-strong "border security force".

While Turkey has long threatened to clear YPG fighters from the Kurdish enclave of Afrin, in north-western Syria, and Manbij, a mainly Arab town to the east, the news appears to have brought those plans forward.