Austria has sent troops to Hungary's border with Serbia following Turkish threats to abandon its deal to stem the flow of migrants into Europe.

Vienna dispatched 60 soldiers to the frontier between the two countries as it emerged the European Union's agreement with Ankara was 'showing cracks'.

Based at Hodmezovasarhely near Szeged in south-east Hungary initially for six months, they will help build roads and erect containers.

Austria has sent troops to Hungary's border with Serbia following Turkish threats to abandon its deal to stem the flow of migrants into Europe. Pictures show a razor wire fence at the Serbia-Hungary border last year

Based at Hodmezovasarhely near Szeged in south-east Hungary initially for six months, they will help build roads and erect containers

It comes after Turkey's foreign minister renewed a threat to scrap the deal if Brussels does not grant Turks visa-free entry to the EU.

The visa waiver is part of a package of incentives the EU offered Turkey to stop migrants heading to Europe.

The main sticking point is an EU demand for Turkey to change the way it defines terrorism.

Turkish Foreign Minister Mevlut Cavusoglu was quoted as telling Swiss daily Neue Zuercher Zeitung: 'Our patience is approaching an end.'

He added that Ankara is upholding agreements and expects the EU to do the same.

Asked when the migrant deal might be suspended, Mr Cavusoglu replied: 'We won't wait until the end of the year.'

Austria's defence ministry said that the soldiers will not be armed or be involved in intercepting people making it past Hungary's border fence with Serbia.

Austria's defence ministry said that the soldiers will not be armed or be involved in intercepting people making it past Hungary's border fence (pictured) with Serbia

Hungary has been criticised by rights groups and others for its alleged mistreatment of refugees and its refusal to take in some of the huge numbers of refugees who arrived in Europe in 2015.

Defence Minister Hans Peter Doskozil said that EU countries needed to do more to protect their borders because the bloc's accord with Turkey risked unravelling.

'In my opinion the cracks in this accord are starting to show,' Doskozil told Oe1 public radio. 'We have a time window in Europe in which to organise ourselves' before the deal collapses, he said.

'Therefore it is right, and high time, that... EU member states recognise this and confront this challenge, deal with the problem themselves and be ready to act themselves.'

Under the EU-Turkey deal in force since March, Ankara agreed to take back migrants who made it to Greece in return for being allowed to send Syrians to the bloc in an orderly redistribution programme.

However Greece has been slow to send migrants back to Turkey. Athens says this is because many have applied for asylum which means that they cannot be moved until the claims are processed.

In addition Greece complains that the EU has failed to provide additional assistance as promised and to share enough of the thousands of migrants around the bloc.