Brussels - The European Union has announced additional funding to help vulnerable migrants in Bosnia, but urged the government there to rebuild a camp that burned down.

Brussels had denounced the living conditions for migrants in Bosnia, a candidate for EU membership, as "completely unacceptable", and warned that lives were at risk.

Fire engulfed the Lipa migrant centre in northwestern Bosnia on December 23. There were no casualties from the blaze but much of the infrastructure was destroyed.

The incident deepened a crisis over where to house thousands of migrants, as Bosnian authorities have failed to find new accommodation for the newly homeless.

In a statement on Sunday, EU foreign policy chief Josep Borrell said Brussels was ready to add another 3.5 million euros to its humanitarian support for Bosnia.

But he warned that 900 people were still exposed on the grounds of the destroyed camp, and that 800 more were without shelter in the region.

"The situation in Una Sana canton is unacceptable. Winter-proof accommodations are a pre-requisite for humane living conditions, which need to be ensured at all times," he said.

"Local authorities need to make existing facilities available and provide a temporary solution until Lipa camp is rebuilt into a permanent facility."

Police believe the blaze was started by migrants to protest the withdrawal of the UN's International Organisation for Migration (IOM), which had been running the camp.

The IOM had left, complaining that the accommodation -- opened in April but without power or running water -- was not fit to house people during the winter.

Bosnia lies on the so-called Balkans route used by migrants heading towards Western Europe as they flee war and poverty in the Middle East, Asia and in Africa.