WARSAW, Poland — The German government says it is cracking down on irregular migration and crime following recent extremist attacks, and plans to extend temporary border controls to all nine of its frontiers next week.

Last month, a deadly knife attack by a Syrian asylum-seeker in Soligen killed three people. The perpetrator claimed to be inspired by the Islamic State group. In June, a knife attack by an Afghan immigrant left a police officer dead and four other people wounded.

The border closures are set to last six months and are threatening to test European unity. Most of Germany’s neighbors are fellow members of the European Union, a 27-country bloc based on the principles of free trade and travel. And Germany — the EU’s economic motor in the heart of Europe — shares more borders with other countries than any other member state.

The Polish prime minister on Tuesday denounced the closures as “unacceptable” and Austria said it won’t accept migrants rejected by Germany.

Here’s a look at some of the issues:

The EU bloc has a visa-free travel area known as Schengen that allows citizens of most EU countries to travel easily across borders for work and pleasure. Iceland, Liechtenstein, Norway and Switzerland also belong to Schengen even though they are not EU members.

According to the EU, member states are allowed to temporarily reintroduce controls at the EU’s so-called internal borders in case of a serious threat, such as one to internal security. But it also says border controls should be applied as a last resort in exceptional situations, and must be time-limited.

Such limitations are often put in place during major sporting events, including the recent Olympic Games in Paris and the European soccer championship this summer.

Nine countries border Germany and all are part of Schengen. Germany already imposed restrictions last year at its borders with Poland, the Czech Republic, Austria and Switzerland.

Germany’s Interior Ministry on Monday ordered the extension of checks at those borders, as well as controls at borders with France, Luxembourg, the Netherlands, Belgium and Denmark.

Interior Minister Nancy Faeser said the aim was to limit irregular migration and protect the nation from “the acute dangers posed by Islamist terrorism and serious crime.”

The government and many Germans welcomed refugees fleeing conflicts in Syria and elsewhere from 2015-16, when more than 1 million asylum-seekers entered the country.

But as large-scale migration to Europe continues nearly a decade later, a backlash is fueling the growth of far-right parties.

Some people say social services are overwhelmed, and extremist attacks by asylum-seekers have led to security fears. It has added up to growing support for firmer immigration policies — and in some cases, backing for the far-right parties that champion such limits.

The unpopular coalition government of Chancellor Olaf Scholz is trying to crack down on irregular immigration after the far right did well in two recent state elections in eastern Germany. Another comes Sept. 22 in Brandenburg, the state surrounding Berlin.

As the EU’s largest economy, Germany is a key trading partner for neighbors. The interior ministry’s announcement has prompted economic worries for the main Dutch transportation lobby group, the Dutch Association for Transport and Logistics. It said the decision was undermining the Schengen principle of free trade and it fears major economic damage.

At home, Germany’s DSLV logistics and freight association urged a selective approach that would spare trucks moving goods across borders — which would mirror what occurred during the European soccer championships. Those checks avoided economic disruptions because officials focused on individuals and not trucks, the association said.

Dirk Jandura, the president of the Federation of German Wholesale, Foreign Trade and Services, said in an statement to The Associated Press that restrictions on the free movement of people “always mean delays and thus cost increases for the economy and especially for wholesale and foreign trade.”

He added: “However, if migration policy findings require restrictive measures, then this is understandable. For us, it is important to implement the measures with a sense of proportion.”

The ruling conservative government in Austria — which is facing a tight race against the far-right party in an election this month — says it will not accept refugees who are turned back from Germany.

Interior Minister Gerhard Karner told reporters that Germany has the right to send people back if another EU country is responsible for their asylum application. But that would require a formal procedure and the consent of the member state concerned.

Meanwhile, Polish Prime Minister Donald Tusk called Germany’s plan “unacceptable” and called for urgent consultations by all countries affected. Poland has struggled with a migration crisis on its border with Belarus since 2021. Warsaw accuses Belarus and Russia of luring migrants from the Middle East and Africa there to destabilize the West.

Agnieszka Łada-Konefał, deputy director of the German Institute of Polish Affairs, said random checks at the German-Polish border create traffic jams that make it more difficult for people to cross for work and discourage Germans from shopping in Poland. Poles also argue that Germany first introduced a policy of openness to refugees but is now pushing them back to Poland.

“Due to the negative perception of the influx of migrants in Poland, any report of migrants being returned by Germany also negatively affects Polish-German relations and Germany’s image in Poland,” Łada-Konefał told the AP.

But in the Netherlands, where the anti-immigration Party for Freedom won last year’s election, the minister for asylum and migration pledged to step up Dutch border controls as well.

Slovenia, Austria and Italy also have extended temporary border controls in some areas or all along their frontiers.

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Associated Press writers Mike Corder in Amsterdam, David McHugh in Frankfurt and Philipp Jenne in Vienna contributed to this report.

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Follow AP migration coverage at: https://apnews.com/hub/migration