Italian police officers used torture on some migrants while trying to process them, an Amnesty International report has claimed.

The rights watchdog also said it had received “consistent accounts that arbitrary detention, intimidation and excessive physical force” had been used to force migrants – survivors of the treacherous Mediterranean crossing – to give their fingerprints to the authorities for processing.

The Italian authorities have strongly denied the allegations.

Fingerprinting is used to identify where migrants first entered the EU and can be used prevent them from moving to different countries. Out of 170 migrants in Italy interviewed by Amnesty, most voluntarily gave their fingerprints and reported no problems, but 24 people alleged having been subjected to ill-treatment by police.

Several others said unnecessary or excessive force had been used to make them give their fingerprints, the group added.

A man named only as Adam, a 27-year-old from Darfur, Sudan, told Amnesty that policemen beat him and subjected him to electric shocks with a stun baton after he refused to provide his fingerprints.

Adam claimed the officers then made him take off his clothes and pulled on his genitals with a tool. “They held me from shoulders and legs, took my testicles with the plier, and pulled twice,” Adam said. “I can’t say how painful it was.”

Refugee crisis - in pictures Show all 27 1 /27 Refugee crisis - in pictures Refugee crisis - in pictures A child looks through the fence at the Moria detention camp for migrants and refugees at the island of Lesbos on May 24, 2016. AFP/Getty Images Refugee crisis - in pictures Ahmad Zarour, 32, from Syria, reacts after his rescue by MOAS (Migrant Offshore Aid Station) while attempting to reach the Greek island of Agathonisi, Dodecanese, southeastern Agean Sea Refugee crisis - in pictures Syrian migrants holding life vests gather onto a pebble beach in the Yesil liman district of Canakkale, northwestern Turkey, after being stopped by Turkish police in their attempt to reach the Greek island of Lesbos on 29 January 2016. Getty Images Refugee crisis - in pictures Refugees flash the 'V for victory' sign during a demonstration as they block the Greek-Macedonian border Refugee crisis - in pictures Migrants have been braving sub zero temperatures as they cross the border from Macedonia into Serbia. Refugee crisis - in pictures A sinking boat is seen behind a Turkish gendarme off the coast of Canakkale's Bademli district on January 30, 2016. At least 33 migrants drowned on January 30 when their boat sank in the Aegean Sea while trying to cross from Turkey to Greece. Getty Images Refugee crisis - in pictures A general view of a shelter for migrants inside a hangar of the former Tempelhof airport in Berlin, Germany Refugee crisis - in pictures Refugees protest behind a fence against restrictions limiting passage at the Greek-Macedonian border, near Gevgelija. Since last week, Macedonia has restricted passage to northern Europe to only Syrians, Iraqis and Afghans who are considered war refugees. All other nationalities are deemed economic migrants and told to turn back. Macedonia has finished building a fence on its frontier with Greece becoming the latest country in Europe to build a border barrier aimed at checking the flow of refugees Refugee crisis - in pictures A father and his child wait after being caught by Turkish gendarme on 27 January 2016 at Canakkale's Kucukkuyu district Refugee crisis - in pictures Migrants make hand signals as they arrive into the southern Spanish port of Malaga on 27 January, 2016 after an inflatable boat carrying 55 Africans, seven of them women and six chidren, was rescued by the Spanish coast guard off the Spanish coast. Refugee crisis - in pictures A refugee holds two children as dozens arrive on an overcrowded boat on the Greek island of Lesbos Refugee crisis - in pictures A child, covered by emergency blankets, reacts as she arrives, with other refugees and migrants, on the Greek island of Lesbos, At least five migrants including three children, died after four boats sank between Turkey and Greece, as rescue workers searched the sea for dozens more, the Greek coastguard said Refugee crisis - in pictures Migrants wait under outside the Moria registration camp on the Lesbos. Over 400,000 people have landed on Greek islands from neighbouring Turkey since the beginning of the year Refugee crisis - in pictures The bodies of Christian refugees are buried separately from Muslim refugees at the Agios Panteleimonas cemetery in Mytilene, Lesbos Refugee crisis - in pictures Macedonian police officers control a crowd of refugees as they prepare to enter a camp after crossing the Greek border into Macedonia near Gevgelija Getty Images Refugee crisis - in pictures A refugee tries to force the entry to a camp as Macedonian police officers control a crowd after crossing the Greek border into Macedonia near Gevgelija Getty Images Refugee crisis - in pictures Refugees are seen aboard a Turkish fishing boat as they arrive on the Greek island of Lesbos after crossing a part of the Aegean Sea from the Turkish coast to Lesbos Reuters Refugee crisis - in pictures An elderly woman sings a lullaby to baby on a beach after arriving with other refugees on the Greek island of Lesbos after crossing the Aegean sea from Turkey Getty Images Refugee crisis - in pictures A man collapses as refugees make land from an overloaded rubber dinghy after crossing the Aegean see from Turkey, at the island of Lesbos EPA Refugee crisis - in pictures A girl reacts as refugees arrive by boat on the Greek island of Lesbos after crossing the Aegean sea from Turkey Getty Images Refugee crisis - in pictures Refugees make a show of hands as they queue after crossing the Greek border into Macedonia near Gevgelija Getty Images Refugee crisis - in pictures People help a wheelchair user board a train with others, heading towards Serbia, at the transit camp for refugees near the southern Macedonian town of Gevgelija AP Refugee crisis - in pictures Refugees board a train, after crossing the Greek-Macedonian border, near Gevgelija. Macedonia is a key transit country in the Balkans migration route into the EU, with thousands of asylum seekers - many of them from Syria, Afghanistan, Iraq and Somalia - entering the country every day Getty Images Refugee crisis - in pictures An aerial picture shows the "New Jungle" refugee camp where some 3,500 people live while they attempt to enter Britain, near the port of Calais, northern France Getty Images Refugee crisis - in pictures A Syrian girl reacts as she helped by a volunteer upon her arrival from Turkey on the Greek island of Lesbos, after having crossed the Aegean Sea EPA Refugee crisis - in pictures Refugees arrive by boat on the Greek island of Lesbos after crossing the Aegean sea from Turkey Getty Images Refugee crisis - in pictures Beds ready for use for migrants and refugees are prepared at a processing center on January 27, 2016 in Passau, Germany. The flow of migrants arriving in Passau has dropped to between 500 and 1,000 per day, down significantly from last November, when in the same region up to 6,000 migrants were arriving daily.

The report said such treatment amounted to torture within the definitions of the United Nations Convention Against Torture. It also said some people were detained arbitrarily, a violation of the Universal Declaration of Human Rights.

The assessment process for arrivals in the hotspots, aimed at selecting asylum seekers from those considered irregular migrants, was also criticised.

"People, often exhausted and traumatized from their journeys and without access to adequate information or advice on asylum procedures, have to answer questions with potentially profound implications for their futures," it said.

Senior Italian police officials were quick to reject the allegations of beatings, electric shocks and sexual humiliation.

"I categorically deny that violent methods are used on migrants both during identification and during repatriation," said Italian police chief Franco Gabrielli. He added that his officers, who work alongside EU officials and human rights groups in the migration centres, had shown enormous responsibility in dealing with the crisis.

Nearly half a million migrants, mainly from sub-Saharan Africa, have reached Italy by boat. Thousands have died attempting the journey in 2016 alone.