The EU said Friday that it was ready to study Hungary's request to be reimbursed for defending Europe's external borders against illegal immigration but urged Budapest to admit its share of asylum seekers.

President Viktor Orban has demanded that Brussels refund half the 800 million euros ($950 million) Hungary says it has spent defending Europe's external borders against illegal immigration.

The European Commission, the executive of the 28-nation European Union, said Hungary had already received financial and practical support from the EU to protect the bloc's external borders.

"If Hungary is now requesting additional support, the commission is ready to quickly examine such a request and provide appropriate assistance if the situation so requires and in accordance with European law," a commission spokesman, Alexander Winterstein, told a press conference.

Winterstein said the EU could help pay for surveillance costs and equipment to manage external borders, but added: "The European Union does not finance the construction of a fence or a barrier at the external borders. That will not change."

While Orban said his country expected Brussels to reciprocate for Budapest's spending, the commission criticised Hungary for refusing to admit asylum seekers under a European solidarity plan.

"But let's not forget one thing. Solidarity is a two-way street and all member states should be ready to contribute," Winterstein said.

"This is not some sort of a la carte menu where you pick one dish, for example border management, while refusing another dish like compliance with relocation decisions."

Hungary has refused to admit its share of asylum seekers under a plan Brussels initiated two years ago to relocate around the EU the 160,000 Syrians, Iraqis and Eritreans who arrived in the frontline countries of Italy and Greece.

Orban has called immigration "the Trojan Horse of terrorism."

In response to a wave of refugees and migrants crossing its border with non-EU Serbia in 2015, Budapest erected a razor-wire fence patrolled by soldiers and dogs.

It then reinforced that barrier with a second fence line, recruited some 3,000 special police and built another fence on its other southern border with Croatia, an EU member outside the passport-free Schengen zone.

Over 400,000 people crossed through Hungary in 2015 but the numbers fell to a trickle after the fences were built. Subsequently the "Balkan Route" northwards from Greece was closed.

The construction drew fierce criticism from Brussels, though other EU member states later built their own versions.