A picture of his heroine, German Chancellor Angela Merkel, is pinned to a tree beside him as he sits on a patch of grass outside a migrants’ hostel in the middle of Europe.

Bearded Syrian Abu Nordine waves his arm at our camera to show off his wristband with the word Germany emblazoned in red on it.

He’s determined to get there, yet at eight in the morning on Thursday this week he was still stuck in Croatia, along with thousands of other migrants.

Duped: Migrants are made to move down the carriages of the train by Slovenian border guards before being sent back to Croatia

Determined: Abu Nordine from Damascus in Syria shows his German wristband as he sleeps rough in Zagreb, waiting for the opportunity to travel to claim asylum

As the hot morning wore on, more migrants kept arriving at the hostel near the centre of Zagreb, the Croatian capital.

They had come through Serbia and, after being turned back at Hungary’s border by police with tear gas and water cannon, they’d chosen an alternative route to Germany through Croatia.

Ahead lay Slovenia, which immediately said any illegal migrants would not be let in and sent riot police to the border to stop them getting through.

‘We will get to Germany one day soon,’ said 38-year-old Abu who claimed to have fled Syria’s capital Damascus after his two children were killed in the country’s brutal civil war. ‘We don’t want to stay in Croatia, and they don’t want us here either,’ he added.

The migrants’ determination follows Mrs Merkel’s contentious announcement a few weeks ago that all Syrians would be welcome in her country. It caused a tidal wave of migrants which has overwhelmed the EU. Unable to cope with the new arrivals, Germany abandoned Europe’s free borders policy and temporarily shut its borders with Austria, before introducing a tougher migrant-vetting regime.

Austria, Slovakia and Holland have also all pledged tighter border controls, while Croatia says it is ‘absolutely full’ and has closed seven of its eight border crossings with Serbia as well as the roads leading to them.

The anarchy now tearing the EU apart is a huge embarrassment for Mrs Merkel whose promise to welcome all Syrians immediately turned the migrant problem into a full-blown crisis — and Croatia is now the front line.

Sleeping rough: Abu Nordine is currently in Croatia but is determined to get to Germany where Angela Merkel said Syrians were welcome

Fan: Abu has a picture of his heroine German Chancellor Angela Merkel on a fan he brought from his home in Syria

Day by day, the migrants are growing more militant. At the Zagreb hostel on Thursday some of the 500 inmates threatened to riot when they found they would be stuck in Croatia because the border with Slovenia was being closed.

A number of young men threw toilet rolls out of the windows, shouting Arabic and English obscenities, and became so threatening that riot police were called.

At the same hostel, I watched hundreds refuse to claim asylum in Croatia because they wanted to do so in Germany. In response, they were handed an official looking document by Zagreb immigration police stating they must leave the European Economic Area (EEA) within 30 days.

With the papers still in their hands, 60 of them then walked out of the hostel’s grounds and down the road as the police watched.

Tense journey: Slovenian border guards stopped the train and made migrants move to carriages 'especially for them' before sending them back to Croatia

Tricked: The migrants from the Porin Hotel Refugee Centre on the outskirts of the Croatian capital were forced on to different carriages, which were uncoupled from the train

Sent back: Slovenian border guards at Dobova moved illegal passengers to the rear two carriages to be returned to Croatia

Security: Slovenian border guards got on the train and segregated migrants from other passengers and returned them to Croatia

‘We are going to Slovenia’, said Halian Hannad, a 34-year-old father of five children, aged between ten and two, who, he told me, are still in his home town of Raqqa, now controlled by ISIS. ‘That is the route to Austria and Germany.’

The 60 migrants walked as far as the bus stop, and then took a ride to the train station.

They bought £7 one-way tickets to Slovenia’s capital Ljubljana and, at 6.37 pm climbed on board. By then they had been joined by nearly 100 other migrants — men, women and a handful of children who had arrived in Zagreb earlier in the day from the border with Serbia.

Outside at the station café, the barman looked on in amazement. ‘We had not seen any migrants in Zagreb until today but we hear thousands more are coming,’ he said. ‘I run a nightclub, and we have brought in extra security staff because there are so many young men with different customs and attitudes to women among them.’

None of this, of course, was of any interest to the migrants on the train as it pulled out towards Dobova, the first town on the Slovenian side of the border with Croatia.

Photographer Jamie Wiseman and I were the only journalists on board. Our fellow passengers grew increasingly excited as the train picked up speed.

Busy: Hundreds of migrants, brought by train from the Serbian border, arrive in Zagreb for processing at the Porin Hotel Centre. On Friday lunchtime the government here announced that over 14,000 had crossed its borders in the past few days

Cramped: Migrants, brought by train from the Serbian border, arrive in Zagreb for processing at the Porin Hotel Centre. On Friday lunchtime the government here announced that over 14,000 had crossed its borders in the past few days, and the situation was 'spiralling out of control'. See Sue Reid Story.

Checks: Locals in Zagreb say thousands of migrants have began appearing in the city

They thought they had escaped Croatia and would soon be in Germany.

But then, soon after 7pm, the train was held at Dobova station. On the platform and on the tracks, 20 Slovenian police officers and border officials surrounded it.

They climbed on board and checked passengers’ passports, before leaving again. But they were not gone for long. After 30 minutes, with the train still stationary, the police boarded again.

They moved through our carriage saying Syrians must move to the back of the train with their luggage.

‘We have carriages which are especially for you,’ said one smiling police officer in crisp blue uniform and lots of gold braid as he gave me what looked suspiciously like a wink, knowing I was British.

Outside on the platform, Dobermans were paraded up and down by their police handlers. Soon it was all over. Tricked, the migrants found the carriages they were now sitting in had been uncoupled and, as the train pulled out, they were left behind.

Influx: A little boy waves to the camera as hundreds of migrants arrive in Zagreb after being brought by train from the Serbian border

Arrivals: Men lean out of the windows on this packed train which has traveled from the Serbian border into Croatia

When they realised they were stranded, the 150 or so migrants in the carriages refused to accept water brought to them by the local Red Cross. When they tried to jump off the train onto Slovenian territory, they were pushed back inside by police and dogs. In the dark of the night, the disgruntled migrants in the two carriages were towed back to Zagreb.

After the incident, trains running between the two capitals were stopped. And Slovenia said it would not allow illegal migrants to pass through to Austria and Germany, although genuine asylum seekers would be allowed through in line with EU rules.

By yesterday, the Slovenians had stepped up road checks near Dobova, using a helicopter as well as foot patrols in the mountainous region.

‘We will return the migrants to Croatia in the shortest time possible,’ said Anton Stubljar, the Slovenian police official in charge of the operation.

We will return the migrants to Croatia in the shortest time possible Anton Stubljar, Slovenian police official

But the fact is that, as I witnessed this week, Croatia is unable to cope with the enormous influx of people — 9,000 are estimated to have arrived on Wednesday alone, and more than 15,000 this week. The two migrant reception centres I visited in and near Zagreb were overflowing by midday on Thursday and still more were arriving.

Further south in Tovarnik, on Croatia’s border with Serbia, a stand-off between migrants and police had grown ugly. Amid desperate scenes at the town’s railway station where migrants who had managed to cross into Croatia had gathered, almost 5,000 had been left stranded overnight after promised trains to Zagreb did not arrive.

Children screamed and women cried as they waited hours before being pushed onto buses for the Zagreb migrant camps. Groups of migrants, almost all of them young and fit-looking men, broke away from the police and set off on foot down railway lines and through fields.

‘They want to take us to the camps, but we don’t want that,’ said Ismail Hussen, claiming — like all the others I asked — that he came from Syria. Whatever the truth of this — and an official EU report released yesterday says only one in five of them is from Syria — the migrants were still trying to get to Germany from Croatia yesterday.

In Zagreb, hundreds continued to wait in vain at the train station, hoping to leave Croatia.

As locals in this staunchly Roman Catholic nation walked by, they stared in astonishment at the newcomers, some of whom were wearing burkhas and full Islamic robes. For their part, the migrants returned the stares with looks of open defiance.

Security: Armed police stand at the Slovenian border as they tighten controls to prevent crossings

Fortress Europe: The Slovenian authorities tighten their border crossing with Croatia as hundreds of migrants from the 14,000 who arrived in Croatia over the past few days begin to try to enter the Schengen area

No way through: Slovenian authorities tighten their border crossing with Croatia as thousands of migrants start to arrive

Other migrants yesterday morning were hiring taxis for Slovenia — only to be stopped at the motorway border-post by Croatian police.

Women in hijabs clutching children stood beside the road in tears and men furiously argued with officials who told them they had to go back as Slovenia would not accept them.

By last night at this border, Slovenia had sent phalanxes of riot police to deal with a growing crowd of migrants running amok.

They were carrying shields, and barricading the border-crossing with wire as lines of hundreds of migrants walked towards them.

At another point on the border with Slovenia, seven miles from Zagreb, a river called the Bregancica divides the two countries. It passes through villages on both sides of the border which are linked by mountain footpaths and narrow bridges.

When I visited yesterday, I spoke to the landlord of a hostelry right next to the river on the Croatian side. I asked him if he expected migrants to escape over to Slovenia by walking.

‘I live in a village just over the river in Slovenia,’ he explained. ‘This summer I have seen African and Middle Eastern migrants running through my own front garden as they slip over the bridges.

‘The border police can’t be everywhere. Up to now, there have been just a few using this route to get through to northern Europe. Soon, I expect, it will be many more.’

And as the migrants’ anger and determination increases daily, there’s every sign he will be proved right.

Crush as thousands try to board train in Tovarnik

At least 2,000 people were stuck in Tovarnik, the first Croatian town after the border with Serbia, awaiting a special train scheduled at midnight that would ferry them onward.

A lack of accommodation in the tiny town added to depleting food and water supplies resulted in a frenzy as the train rolled in.

Men, women and children clambered to board the carriages headed to Beli Manastir in eastern Croatia.

Crush: A stampede occurs as Middle Eastern refugees rush to find space on a train headed to Beli Manastir

Desperate: Migrants rush to board a train in the eastern-Croatia town of Tovarnik, close to the border between Croatia and Serbia

Rush: Middle Eastern refugees rush to find space on a train headed to Beli Manastir from Tovarnik, in Croatia

The migrants, mostly from poor or war-torn countries in the Middle East, Africa and Asia, have streamed into Croatia since Wednesday, after Hungary blocked what had been the main route with a metal fence and riot police at its border with Serbia.

Croatia, offering an overland route to Germany bypassing Hungary, found itself suddenly overwhelmed, with the arrival of more than 17,000 people since Wednesday morning.

Hundreds of thousands have been trekking across the Balkan peninsula to reach the richer European countries to the north and west, especially Germany, which is preparing to accept 800,000 migrants this year.

But that has wrongfooted the European Union, which has come up with no common policy to deal with the biggest wave of migration to Western Europe since World War Two.

Crowds: Migrants rush to board a train in the eastern-Croatia town of Tovarnik, close to the border between Croatia and Serbia

Appeals for calm: Migrants jostle to get on the train as they try to get across Croatia en route to Germany