Sweden's minister of justice Morgan Johansson said Sweden will challenge Hungary in court unless it starts taking back asylum seekers from other EU countries.

The European Commission is sending a fact-finding delegation to Hungary to examine reasons for the row.

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Earlier this month, ministers from the Nordic countries - Denmark, Finland, Iceland and Norway, in addition to Sweden - wrote to the EU executive to complain that Hungary is not abiding by EU Dublin rules, which say refugees should in principle seek asylum in the first EU country they enter.

Johansson was one of the co-signatories of the letter.

He told Swedish radio that EU migration commissioner Dimitris Avramopoulos replied this week, saying Hungary must comply with the regulation and should examine asylum claims of those people who were first registered there and later travelled on to other countries.

”The commission is the guardian of the EU treaties. It has to ensure that governments stick to agreements they once signed up to,” Johansson said.

Otherwise, Sweden would take Hungary to the European Court of Justice (ECJ), he added.

More than 1 million people came to Europe last year. Many were first registered in Hungary.

The Swedish Migration Agency says it has around a thousand asylum seekers who were first registered in Hungary waiting to be transferred back.

But Hungary claims the refugees first entered the EU through Greece, making Greece responsible for examining their claims.

Government’s spokesman Zoltan Kovacs recently told reporters in Brussels that Hungary would refuse to accept returns of asylum seekers from other EU states.

"We are not going to take responsibility for the shortcomings of other countries," he said.

The Dublin regulation says an EU country has six months to transfer a person to another EU state, if it finds that country to be responsible for an asylum claim.

But if the transfer is not made within that timeframe, it becomes responsible itself for the asylum seeker.

The Nordic countries are not the only ones to accuse Hungary of not complying with the Dublin regulation.

Austria threatened to take Budapest to court already earlier this month for its refusal to take back asylum seekers. Slovakia said in July it stopped trying to send back people, because efforts to do so were in vain.