Bangkok, Thailand: Two journalists, including an Australian editor, went on trial in Thailand Tuesday over a report they published implicating the navy in human trafficking, as the United Nations urged the junta-ruled nation to drop the case.

Alan Morison and his Thai colleague Chutima Sidasathian of the Phuketwan news website could face up to two years in jail for criminal defamation and five years for breaching the Computer Crimes Act if they are found guilty.

The charges, brought last year, relate to an article in July 2013 by Phuketwan quoting an investigation by Reuters news agency which said some members of the Thai navy were involved in trafficking Rohingya Muslim asylum-seekers who had fled Myanmar.

Reuters has not been charged over its reporting -- part of a series honoured with a Pulitzer Prize last year -- and rights groups have accused the navy of trying to muzzle a small media outlet.

The trial, which opened at Phuket Provincial Court on the southern island Tuesday, is expected to begin with testimony from four witnesses called by the prosecutors and a verdict is due within 30 days.

Speaking to AFP ahead of the trial, Morison said: ‘We do not understand why the military government has not withdrawn the case.

‘The initial pursuits against Reuters were dropped. We quote exactly the same paragraph (They are pursuing us) for only one paragraph reproduced word-to-word from Reuters.’

On Tuesday the United Nations Human Rights Office urged Thailand to drop the charges against the two journalists.

‘Freedom of the press, including freedom for journalists to operate without fear of reprisals, is essential in promoting transparency and accountability on issues of public interest,’ it said in a statement.

Tens of thousands of the stateless Rohingya, one of the world's most persecuted minorities, have fled Buddhist-majority Myanmar's western Rakhine state since 2012, when deadly unrest erupted.

In recent years they have increasingly been joined on dangerous sea crossings by economic migrants from neighbouring Bangladesh with their rickety wooden boats mainly headed for Malaysia.

In May a Thai crackdown on the lucrative smuggling industry saw traffickers abandon their human cargo at sea, sparking a regional migrant crisis.

Around 4,500 Rohingya and Bangladeshi migrants were stranded in Southeast Asian waters and ping-ponged between countries reluctant to accept them until they eventually landed ashore on Malaysian, Indonesian, Bangladeshi, Myanmar and Thai soil.

Thailand has seen a rapid erosion of civil liberties -- including a ban on political protests and any criticism of the ruling regime -- since the military seized power from an elected government in May 2014.

Its southern provinces have long been known as a nexus for people-trafficking and rights groups have accused Thai officials of both turning a blind eye to the trade -- and even complicity in it.

Dozens of people have been detained in the recent crackdown including some local officials and Manas Kongpan, a senior military officer accused of being a major smuggling kingpin.