For the fifth time in one week, Sami, a 25-year-old from Guinea, was trying to cross into France from the Italian border town of Ventimiglia.

As the train glided along a track sandwiched between the steep cliffs of the Maritime Alps and a glistening Mediterranean sea, passing well-manicured beach resorts along the way, he was feeling hopeful. “I just need to get as far as Marseille where I have a friend who can help me reach Germany,” he told the Observer. “All I want is a better life – in Guinea it is impossible, it is so corrupt.”

But, after a week of thwarted attempts to cross an impenetrable border, Sami’s plan was scuppered once again by border police at Menton-Garavan, the first stop along a route that passes through Monaco and Nice before arriving in Cannes.

Along with three others, he was escorted off the train and immediately recognised by an officer who had intercepted him the day before. Tourists aboard the train looked on in bewilderment.

“On some days we find between 10 and 20 migrants on each train,” said the officer leading the team of four. “We are doing nothing wrong in sending them back; it’s within the law. They are supposed to stay in the country in which they first arrived.”

This game of cat-and-mouse has played out between France and Italy since early 2011, shortly after the Arab spring and Syrian war prompted the biggest migration crisis since the second world war. Between January and May this year alone, French authorities say they sent back 10,524 people who tried to cross either by train, or by walking along the motorway or a deadly mountain path.

The situation reached boiling point last week when Emmanuel Macron, the French president, was accused of “hypocrisy” by Giuseppe Conte, Italy’s new prime minister, after he criticised his southern neighbour for blocking the Aquarius from Italian ports. The rescue ship had saved more than 600 people from the sea off Libya. The order came down from Matteo Salvini, the recently installed anti-migrant interior minister and leader of the far-right League, which is now in government with the populist Five Star Movement.

Relations between Macron and Conte appeared to have thawed on Friday in Paris, where they called for the EU to establish asylum processing centres in Africa as a way of stopping the flow of migrants across the Mediterranean.

But in the perennial migrant waiting room of Ventimiglia, a seaside town which has become known as the “Calais of Italy”, charity workers are unconvinced. “Where will they set up these centres? Definitely not in Libya,” said Daniela Zitarosa, from the Italian humanitarian agency Intersos. “You can’t exactly put centres in countries from where asylum seekers escaped because their lives were in danger.”

Facebook Twitter Pinterest About 500 migrants are staying in a Red Cross camp on the outskirts of town. Photograph: Miguel Medina/AFP/Getty Images

Zitarosa contributed testimony to a report released by Oxfam on 15 June accusing French border police of detaining migrant children as young as 12 without food or water, cutting the soles off their shoes and stealing sim cards from their mobile phones before illegally returning them to Italy. The allegations came two months after French police were accused of falsifying the birth dates of migrant children on “refusal of entry” documents so they could pass them off as adults and send them back.

Under the Dublin regulation, child migrants in France cannot be sent back to Italy if they request asylum. EU law stipulates that unaccompanied minors must be protected, and that those seeking asylum in one member state have the right to be transferred to another where they have family members.

The police officer at Menton-Garavan dismissed the claims as “completely false”. He said: “If that’s what they say, that’s what they say … we’re just here doing our job, monitoring the trains.”

At least 16 migrants have died while trying to cross into France since September 2016, either by falling off the mountain path or being hit by cars. A migrant was recently electrocuted after climbing on top of a train, the police officer said.

Some 16,500 people, a quarter of them children, had passed through Ventimiglia in the nine months to April, according to the Oxfam report. About 500 are currently staying in a Red Cross camp on the outskirts of the town. Local authorities recently dismantled a makeshift camp beneath an underpass along the banks of the Roia river. Meanwhile, a priest who had been hosting people in a church opposite was forced to stop after receiving threats.

Zitarosa estimates around 200 migrants are sleeping rough, in parks or on the beach. She said there had been an increase in arrivals in recent weeks as the summer approached: “You hear stories every day from people who have suffered … starting from personal accounts in their home countries and then their experience in Libya and the sea crossing,” she added.

“ Then, in Ventimiglia, they are being pushed back and suffer even more. It’s not an easy job and it makes me feel deeply sad. With all the political stuff I feel even more worried about the future as these people are not being treated like human beings – politics is being made out of people and it needs to stop.”

For Sami, who arrived in Italy by boat and had been sleeping for more than a week in a park in Ventimiglia, yesterday’s setback did not mark the end. He is determined to make it to Germany and find work. “This is my fifth time,” he said. “I will keep trying.”