BUDAPEST (Reuters) - Hungary plans to detain migrants while their asylum requests are assessed, a ruling party lawmaker said on Wednesday, a proposal that human rights campaigners said could be illegal.

A migrant carrying a child falls after being tripped over by TV camerawoman Petra Laszlo (R) while trying to escape from a collection point in Roszke village, Hungary, September 8, 2015. REUTERS/Marko Djurica/File Photo

The plan will be part of the spring legislative agenda of the Fidesz party of Prime Minister Viktor Orban, whose popular hardline stance on immigration may help him retain power at an election early next year.

Under the plan, migrants whose asylum applications are not immediately rejected would no longer be allowed to move freely while their requests are processed, Fidesz parliamentary group leader Lajos Kosa told a news conference.

“Now there will be two options. If they meet certain criteria, then they could be detained. If not, we will create a hot spot where they will need to wait for authorities to process their asylum requests,” Kosa said.

Migrants would be detained close to the border, he said, but did not explain whether the government would set up new camps or what the “hot spots” would look like.

The Hungarian Helsinki Committee human rights group said the measure could violate international law if migrants are detained en masse.

“Neither European Union law nor the European Convention on Human Rights nor Hungarian legislation allow the mass detention of asylum seekers without individual examination and justification,” it said on its website.

“If an asylum seeker is suspected of being a terrorist, then they can and should be taken into custody during the asylum request procedure,” it said. “However, all asylum seekers or even their majority ... cannot be locked up on this basis.”

Hungary has been a focal point of the migration crisis, with hundreds of thousands passing through in 2015 in often chaotic scenes on the frontier with Serbia - the external border of the EU’s passport-free Schengen area - and a Budapest rail terminus.

A new steel fence along Hungary’s southern frontier and tightened checks have reduced the number of migrants let through at each southern checkpoint to just 10 people a day, creating a bottleneck in Serbia.