The United Nations stepped up criticism of Australia’s refugee detention policy on Friday, warning there was “no empirical evidence” that locking up asylum seekers deterred irregular migration.

Speaking as fresh riots broke out in the remote Christmas Island detention centre, the UN’s refugee agency UNHCR said it was deeply concerned about the impact of mandatory detention on the wellbeing of detainees.

Richard Towle, UNHCR representative in Australia, said research into alternative refugee models had found “no empirical evidence at all that detention deters irregular migration”.

“In the Australian context, UNHCR has longstanding concerns that mandatory detention for prolonged periods, particularly in isolated locations and crowded conditions, can quickly impact on the psycho-social health and welfare of asylum-seekers and refugees,” Mr Towle said.

“We hope that... Australia will consider exploring alternatives to detention for other asylum seekers who pose no identified health or security risks to the community.”

Mr Towle pointed to an April report into alternatives to detention which showed it cost AU$339 (248.64) per day to keep a refugee locked up, versus between AU$7 and AU$129 for them to live in the community.

Less than 10 per cent of asylum applicants sent into the community fled when released to proper supervision and facilities, according to the report.

It said government policy “cannot be based on assumptions about likely migrant behaviour and must be instead based on empirical evidence”, of which there was little regarding the effectiveness of detention.

“Pragmatically, no empirical evidence is available to give credence to the assumption that the threat of being detained deters irregular migration, or more specifically, discourages persons from seeking asylum,” UNHCR said.

“Global migration statistics have been rising regardless of increasingly harsh governmental policies on detention.”

Overcrowded by a record influx of 6,900 boatpeople last year, Australia’s refugee centres have been rocked by protests and riots, the most recent of which, on Thursday night, involved up to 100 de­tainees.

Canberra is finalising a contentious plan to send 800 boat people to Malaysia for processing in exchange for accepting some 4,000 of the Southeast Asian nation’s already registered refugees.

The proposal has sparked controversy with concerns that the group could be mistreated with Malaysia not a signatory to the UN refugees convention.