German states spent more than €20bn (£17.5bn) on refugees in 2016, government figures have indicated as Angela Merkel continues to come under pressure for her policy on migration.

Statistics seen by The Independent for the states of Bavaria, Schleswig-Holstein, Hesse and Berlin show that the cost of housing and integrating asylum seekers has far outstripped official predictions.

The Bundestag’s statistics service has listed a total spend of over €7bn (£6bn) for those four states alone in 2016, meaning the nationwide figure is likely to be far higher.

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Johannes Singhammer, Vice President of the German parliament, told Die Welt: “[The figures] show that if the costs are added up for all federal states, around €23bn (£20bn) has probably been spent on migrants and refugees in 2016.”

The four states recorded have taken around a third of asylum seekers currently living in Germany, where more than a million have arrived since the start of the refugee crisis in 2015.

Berlin set aside €685m (£600m) for accommodation, unaccompanied minors, integration programmes, healthcare, language lessons and other projects but spent around €1.3bn (£1.1bn) in total – almost double the budget.

The state of Bavaria spent €3.3bn (£2.9bn), Hesse €1.6bn (£1.4bn) and Schleswig-Holstein €783.7m (£685.9m).

A spokesperson for the Bundestag’s statistics authority said a complete report would be made public when other states had calculated their spending.

An official survey conducted in December 2015 predicted that federal states would spend €17bn (£15bn) on dealing with the refugee crisis in the following year but with a huge backlog of asylum claims and difficulties with deportation, costs have spiralled beyond expectations.

Germany’s government has drawn up a new package of refugee funding for state authorities, as well as plunging money into new housing construction to prevent migrants sleeping in emergency accommodation like school gymnasiums and military barracks.

Refugees settle in Germany Show all 12 1 /12 Refugees settle in Germany Refugees settle in Germany Germany Mohamed Zayat, a refugee from Syria, plays with his daughter Ranim, who is nearly 3, in the one room they and Mohamed's wife Laloosh call home at an asylum-seekers' shelter in Vossberg village on October 9, 2015 in Letschin, Germany. The Zayats arrived approximately two months ago after trekking through Turkey, Greece and the Balkans and are now waiting for local authorities to process their asylum application, after which they will be allowed to live independently and settle elsewhere in Germany. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity 2015 Getty Images Refugees settle in Germany Germany A refugee child Amnat Musayeva points to a star with her photo and name that decorates the door to her classroom as teacher Martina Fischer looks on at the local kindergarten Amnat and her siblings attend on October 9, 2015 in Letschin, Germany. The children live with their family at an asylum-seekers' shelter in nearby Vossberg village and are waiting for local authorities to process their asylum applications. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity Getty Images Refugees settle in Germany Germany Kurdish Syrian asylum-applicant Mohamed Ali Hussein (R), 19, and fellow applicant Autur, from Latvia, load benches onto a truckbed while performing community service, for which they receive a small allowance, in Wilhelmsaue village on October 9, 2015 near Letschin, Germany. Mohamed and Autur live at an asylum-applicants' shelter in nearby Vossberg village. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity Getty Images Refugees settle in Germany Germany Mohamed Ali Hussein ((L), 19, and his cousin Sinjar Hussein, 34, sweep leaves at a cemetery in Gieshof village, for which they receive a small allowance, near Letschin Getty Images Refugees settle in Germany Germany Mohamed Zayat, a refugee from Syria, looks among donated clothing in the basement of the asylum-seekers' shelter that is home to Mohamed, his wife Laloosh and their daughter Ranim as residents' laundry dries behind in Vossberg village on October 9, 2015 in Letschin, Germany. The Zayats arrived approximately two months ago after trekking through Turkey, Greece and the Balkans and are now waiting for local authorities to process their asylum application, after which they will be allowed to live independently and settle elsewhere in Germany Getty Images Refugees settle in Germany Germany Asya Sugaipova (L), Mohza Mukayeva and Khadra Zhukova prepare food in the communal kitchen at the asylum-seekers' shelter that is their home in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Efrah Abdullahi Ahmed looks down from the communal kitchen window at her daughter Sumaya, 10, who had just returned from school, at the asylum-seekers' shelter that is their home in Vossberg Getty Images Refugees settle in Germany Germany Asylum-applicants, including Syrians Mohamed Ali Hussein (C-R, in black jacket) and Fadi Almasalmeh (C), return from grocery shopping with other refugees to the asylum-applicants' shelter that is their home in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Mohamed Zayat (2nd from L), a refugee from Syria, smokes a cigarette after shopping for groceries with his daughter Ranim, who is nearly 3, and fellow-Syrian refugees Mohamed Ali Hussein (C) and Fadi Almasalmeh (L) at a local supermarket on October 9, 2015 in Letschin, Germany. All of them live at an asylum-seekers' shelter in nearby Vossberg village and are waiting for local authorities to process their asylum applications, after which they will be allowed to live independently and settle elsewhere in Germany 2015 Getty Images Refugees settle in Germany Germany Kurdish Syrian refugees Leila, 9, carries her sister Avin, 1, in the backyard at the asylum-seekers' shelter that is home to them and their family in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Somali refugees and husband and wife Said Ahmed Gure (R) and Ayaan Gure pose with their infant son Muzammili, who was born in Germany, in the room they share at an asylum-seekers' shelter in Vossberg village on October 9, 2015 in Letschin, Germany. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity, and are waiting for authorities to process their application for asylum 2015 Getty Images Refugees settle in Germany Germany German Chancellor Angela Merkel pauses for a selfie with a refugee after she visited the AWO Refugium Askanierring shelter for refugees in Berlin Getty Images

Despite the huge financial cost of the ongoing crisis, Germany’s federal government announced a budget surplus of €6.2bn (£5.4bn) last year.

The unprecedented number of refugees arriving in 2015 generated a huge backlog of claims that civil servants are still working to clear, with more than 430,000 cases outstanding at the start of 2017.

Thomas de Maizière, the German interior minister, said about 55,000 migrants returned home voluntarily, compared with 35,000 in 2015, while another 25,000 were forcibly deported.

Last month, the government announced a scheme to offer migrants financial incentives of up to €1,200 (£1,000) each to leave Germany and withdraw their application for protection, with a lower amount of €800 (£700) if they choose to depart after being refused asylum.

Mr de Maizière said StarthilfePlus was intended for those with “very poor chances of success” under the country’s asylum laws.

“I appeal to understanding and reason: For all those who have no prospect of staying in Germany, voluntarily departure represents a better way than deportation,” he added.

The flow of asylum seekers into the country has fallen dramatically since the implementation of the controversial EU-Turkey deal last March, which aimed to slow boat crossings to Greece by seeing anyone arriving detained under threat of deportation.

The number of new applications plummeted by more than 600,000 last year, standing at less than a third of those at the height of the crisis, when Ms Merkel opened Germany’s borders to Syrian refugees amid a series of boat disasters in the Mediterranean and Aegean seas.

Children play in a building converted into refugee accommodation in Frankfurt (EPA)

Her policy sparked the arrival of more than a million asylum seekers in Germany, many of whom are still housed in temporary accommodation while awaiting a government decision.

Anti-immigration and far-right groups have criticised the decision, blaming the Chancellor for a series of Isis-inspired terror attacks carried out by migrants in Germany last year, including the Berlin Christmas market massacre.

The atrocities and increasing concern over migration have driven surging support for the populist Alternative for Germany (AfD) party, which is expected to enter the national parliament (Bundestag) for the first time as Ms Merkel battles for a fourth term in September’s election.

There was fresh scrutiny this week after Germany’s federal prosecutor charged three suspected Isis members with planning a terror attack in Düsseldorf.

Officials said the two of the Syrian men, aged between 25 and 27, investigated smuggling routes to Europe for jihadis in 2014, sending several refugees as tests before journeying along the migrant route themselves in 2015.

They allegedly drew the third suspect into the plot and worked with an Isis bomb maker already deployed to Germany by commanders, planning to detonate two suicide bombs in Düsseldorf’s popular Old Town before other militants massacred as many passers-by with guns as possible.

The plan was thwarted after one of the conspirators turned himself into French authorities in February last year.