The EU Commission has expressed concerns over Hungary's new and amended migration laws in a letter sent last week which asked for clarification.

The letter, published earlier by Hungarian media and now on Statewatch, a non-profit organisation committed to transparency, was sent on 7 October and was signed by the Commission's director general for migration and justice.

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The letter challenges recent Hungarian legislation that seems to fast-track people seeking refuge back to Serbia with a ban on entering the EU for a year.

"Applications for international protection made at the border in a border procedure are systematically declared inadmissible on the basis of the fact that applicants have transited through Serbia," the letter states.

It asks the Hungarian authorities to explain how the new border management is compatible with EU law, as reportedly only around 100 people are registered at the transit zone daily along the Serbian border and a decision dismissing their request can be made within an hour.

The Commission is concerned that asylum seekers are not interviewed by the authorities, their story is not being heard and they have no means to challenge the concept of Serbia being a "safe country".

The EU executive is also worried about reports that people are not given proper information free of charge and have difficult access to free legal assistance, or interpretation.

It also questions the circumstances of detention for asylum seekers, who are not told why they are being detained and how can they appeal against their detention.

The Commission expresses serious concerns over how asylum seekers can fully exercise their right to challenge the rejection of their application, given the lack of information, legal assistance and short deadlines.

The letter also asks for figures on how many requests for international protection were dismissed, how many of them were appealed, and how many concern children and other vulnerable asylum seekers.

The Hungarian authorities have two weeks to reply, and further communication is expected before the Commission could open an official investigation into whether the Hungarian legislation is in line with EU law.

The Commission is concerned about the lack any specific procedure or safeguards for children, and whether illegal border crossings are not dealt with unproportionally, with the possibility of up to eight years prison sentence for damaging the border fence.

The Commission is also concerned about the use of military in managing the borders and says that their conduct must respect EU rules.

Hungary's government tweaked legislation in July and September to set up and protect the border fence along the Serbian frontier, sped up asylum procedures and gave extra rights to police and military in border management.

More than 320,000 people fleeing war and persecution have crossed into Hungary so far this year, with most headed to Austria and Germany.

Since Hungary put up the razor fence in August, hundreds continued to climb over or crawl under it even after the new legislation came into force on September 15.

There have been more than 400 fast-track trials of migrants since then, mostly Syrians and Iraqis, charged with the crime.