Image copyright Family photos Image caption Hannah Witheridge and David Miller were killed in Koh Tao

UK police officers are to travel to Thailand to help investigate the murders of two British tourists found dead on the island of Koh Tao.

The country's military ruler dropped objections to accepting help in the case after being pressed on the issue by UK Prime Minister David Cameron.

The bodies of David Miller, 24, and Hannah Witheridge, 23, were discovered on a beach on 15 September.

Two Burmese men are under arrest but the Thai inquiry has been criticised.

The UK Foreign Office summoned the Thai charge d'affaires earlier this week to express concern about the police investigation.

Zaw Lin and Win Zaw Htun, both migrant workers from Myanmar, also known as Burma, are alleged to have confessed to the killings earlier this month.

Image copyright EPA Image caption Zaw Lin (left) and Win Zaw Htun are seen here leaving Koh Samui provincial court

Police have denied subsequent reports that the pair, both aged 21, then withdrew their confessions.

The two suspects were in court for a pre-trial witness hearing on the island of Koh Samui on Tuesday, but did not testify.

They are charged with conspiracy to murder, conspiracy to rape and robbery, and could face the death penalty if found guilty.

'Areas of concern'

Thai Prime Minister Gen Prayuth Chan-ocha met Mr Cameron at a summit in Italy and agreed that a delegation of British officers could travel to Thailand, having previously rejected offers of assistance.

A diplomatic source said that Thai authorities were leading the investigation, but it was important that the victims' families could be reassured about the justice process.

He said: "There are two areas we are particularly concerned about. One is the verification of the DNA samples of the suspects, making sure there is further independent verification.

"And the second is the investigation into allegations of mistreatment of the suspects.

"What the PM secured was agreement from the Thai PM that we can send some British police investigators to Koh Tao to work with the Royal Thai Police on this."

Image copyright Reuters Image caption The case was discussed by the Thai and UK leaders in Milan

The discussion between the leaders came at the Asia Europe Meeting in Milan.

Post-mortem examinations found Mr Miller, from Jersey, died from drowning and a blow to the head, while Miss Witheridge, from Great Yarmouth, died from head wounds.

Police have said DNA found on Ms Witheridge matched samples taken from the suspects.

Concerns about the murder investigation include the fact the crime scene was not sealed off after the killings, as well as the fact an early statement was released by police saying that no Thai person could have committed such a crime.

Mr Zaw's mother Phyu Shwe Nu has said her son was being made a "scapegoat" by police.