Bangkok, Thailand: A high-ranking Thai army officer wanted on human smuggling charges handed himself into police Wednesday, the first military figure in the junta-ruled kingdom to be arrested over the grim trade.

Lieutenant General Manas Kongpan voluntarily attended police headquarters in Bangkok on Wednesday morning.

His detention raises awkward questions for junta chief Prayut Chan-O-Cha, who has repeatedly justified his coup last year as a much-needed antidote to graft that he says had flourished under a series of elected civilian governments.

Manas, a long-serving army officer in Thailand’s south, arrived at police headquarters dressed in his military uniform and made no statement to a waiting press pack.

But the country’s top police officer said the 58-year-old denied the charges against him.

‘(He) contacted me to surrender and to fight the case,’ national police chief Somyot Poompanmoung told reporters.

‘He said he has no involvement in the case—in other words he denied the charges,’ Somyot added.

Thai police have yet to detail what role Manas is alleged to have played in the country’s once thriving people smuggling and human smuggling trade.

Rights groups have long accused Thai officials of turning a blind eye to—or even complicity in—the trade of migrants through its southern provinces and into Malaysia, but until now no military personnel have been implicated.

Thai police say they have issued 84 arrest warrants in connection with their people smuggling and human smuggling investigation, with 51 suspects detained so far, including some local officials.

Southern Thailand has long been known as a nexus for lucrative and largely unchecked smuggling networks through which persecuted Rohingya Muslims in Buddhist-majority Myanmar, and Bangladeshi economic migrants, amongst others, would pass on their way to Malaysia.

The extent of the trade—and the brutality of gangmasters who ran it—was laid bare last month when a Thai crackdown led to the discovery of scores of jungle prison camps on both sides of the Thailand-Malaysia border that were run by smuggling gangs.

So far more than 150 graves have been uncovered in the camps where many victims were held for months in miserable conditions until relatives paid hefty ransoms for the release of their loved ones.

In recent weeks around 4,500 hungry and bedraggled migrants have arrived on Thai, Malaysian, Indonesian, Bangladeshi and Myanmar soil after the crackdown threw smuggling routes into disarray.

According to the Royal Thai Army website, Manas was the commander of the upper south province of Chumphon in 2013, before taking a senior position in Songkhla, which borders Malaysia.

He was moved this year to the Royal Thai Army Headquarters in Bangkok to act as an adviser—although it was not immediately clear in what capacity.

The army has suspended Manas and launched an internal probe since the arrest warrant was issued against him on Sunday.