Thousands of migrants are gathered at Turkey's border with Greece, after the Turkish government last week allowed the refugees passage to Europe saying it had "reached its capacity."

The move tramples on a 2016 deal struck with the European Union to halt migrants travelling from the Middle East towards Europe.

It comes on the back of an airstrike by Russian-backed Syrian forces on the city of Idlib in the neighbouring country last week, killing 33 Turkish soldiers. Turkey's about-face is seen as a way of leveraging European support for its military operation in Syria.

CNN Senior International Correspondent Arwa Damon and journalist Murat Baykara are at the Pazarkule Border post between Turkey and Greece. They explain the situation on the ground:

What's happening on the Turkish border with Greece?

The images are horribly reminiscent of the refugee flood in 2015: thousands of refugees, camped out in the open, are clinging to a sliver of hope that they will be able to cross into Europe.

This was sparked by Turkey on Thursday saying it would no longer stop refugees from attempting to cross by land or sea into Greece.

Back in 2016, when the masses were taking the refugee trail from Turkey across the EU, the two powers struck a financial aid deal to stem the flow.

But Europe never really paid up. And Turkey, hosting upwards of 3.5 million refugees, mostly from Syria, has long threatened to open its borders if left to shoulder the refugee burden alone.

Why has Turkey opened the border now?

The news that Turkey would be opening its northern borders with Europe emerged shortly after 33 Turkish soldiers were killed in Idlib province in multiple strikes on their convoy.

Turkey is using its huge refugee population as leverage against Europe to garner support for its military operation to keep Syrian President Bashar al-Assad's forces — backed by Russia and Iran — from gaining more territory inside Idlib.

Since December, around 1 million people have been displaced inside Idlib, moving closer to the border with Turkey, creating a humanitarian crisis along Turkey's southern border.

Turkey says it is already beyond capacity when it comes to refugees. And so part of this decision is to clear space, should it decide to open that southern border with Syria.

How have Greek authorities reacted?

Greece has stood firm, not opening its side of the border and beefing up its presence along it.

Migrant youths often clash with Greek border guards, who fire tear gas when they attempt to storm the border. Others huddle around fires with their children trying to stay warm.

Some refugees attempt to cross the river into Greece. Turkey claims that more than tens of thousands have already crossed into Greece, which is encouraging more people to move towards the border. But Greece says that very few people are making it through.

Some groups whom CNN spoke to say Greek personnel forced them back to Turkey, smashed their phones, ripped up their IDs, and beat them.

The Greek authorities deny this behaviour, although this is something that refugees trying to cross into the country have long accused them of.

Where do the refugees want to go and why?

The aim is Europe; the ultimate goal is the pursuit of a better life and opportunities.

We met refugees from Afghanistan, Iran, Pakistan, Syria, Iraq, Morocco and Somalia. Some are new arrivals to Turkey who came just waiting for a chance like this.

Others have been in Turkey for years but struggled to find work, housing, and education for their children, especially as Turkey's economy took a downward spiral and the cost of living surged.

What's the situation like for migrants now?

It is desperate and sad. Thousands have been waiting at the border for days. They have no shelter. Temperatures dip below zero at night and it's been raining, so people have been chopping wood from the nearby forest to stay warm.

Many of the children are sick, and the elderly are struggling. They left where they were staying in Turkey with just what they can carry so they depend on food aid: this amounts to little more than bread and soup handouts, but there's not enough to go around. Yet many say they are ready to risk it all and carry on waiting.

Some know that they are being used as leverage, as political pawns. Others believe that both sides of the border are open — or that at least when they reach Europe's gates, they will be allowed to cross.

What's Russia got to do with it all?

For Turkey, what's happening in Idlib and the potential for another Syrian influx is creating a crisis. Turkey, unlike the West, does not have the luxury of turning away from what is happening in Idlib or from the refugee crisis.

Turkey wants to prevent a humanitarian disaster in Syria, avoid another refugee flow from that country, and preserve what's left of the Syrian opposition along with the possibility of a genuine political process.

In February, Turkey lost more than 50 soldiers in Idlib. At the moment it's facing off with regime forces and their Russian backers on its own. The United States, EU and NATO have issued statements of solidarity, but do little else to help on the military or humanitarian fronts.

By opening its borders, Turkey is calculating and hoping for renewed support that extends beyond the rhetoric we have heard so far from the US and the EU; both have been ready to go the extra mile just to keep refugees and migrants out of their own countries.

What happens next?

It gets uglier. We now have a situation where the lives of the most vulnerable are again being manipulated and used as bartering chips.

What is happening at Turkey's northern border with Europe is tied with what is happening at its southern border with Syria. An attempt to control a humanitarian crisis in Syria could ultimately result in another emergency along its border with Greece.

More people have been arriving at the border hoping to make it across.

But it's unlikely that Europe will fold to the pressure, no matter how many arrive at its front door.