The British government is in talks with Indonesia over the disappearance of half a dozen sunken warships illegally salvaged from the Java Sea, together with the remains of hundreds of Dutch and British sailors.

British diplomats met the Indonesian maritime ministry in Jakarta to discuss the missing wrecks last week, and is now coordinating with authorities in a related investigation, an embassy spokesperson in Jakarta has confirmed.

The discovery that the vessels, including six Dutch and British warships that were sunk in the 1942 Battle of the Java Sea, were missing has sparked international condemnation.

The sites are considered sacred war graves and under international law are recognised as the property of the flagged nation.

A mass salvaging operation in the waters of south-east Asia in the past three years has seen up to 40 second world war-era vessels vanish, pillaged for valuable bronze, copper, brass and unique old steel.

In Brondong, east Java, discovery of the illegal salvage mission has been followed by distressing allegations the bones found in the old ships were unceremoniously dumped in an anonymous mass grave.

Indonesian authorities have excavated three sites in Brondong in recent weeks where human remains are believed to be located.

In close coordination with representatives from the Dutch embassy and its war graves commission, the British embassy says it is currently awaiting requests for technical assistance from Indonesian authorities in its investigation into the missing ships and origin of the bones.

Assistance provided could be forensic, archaeological or scientific in nature, the spokesperson told the Guardian.

It is understood samples of bones from the mass grave at Suko cemetery, a graveyard close to Brondong port where the salvaging mission was allegedly carried out, have been taken for forensic testing.

The Dutch government, which has been lobbying Indonesia on this issue in a series of joint meetings for the past year, is also sending an expert military team to assist.

The Dutch ministry of defence team is scheduled to arrive in Indonesia on Wednesday.

News of the investigation’s progress comes as Plymouth MP Luke Pollard launched an online petition calling on the government to ensure the remains of Royal Navy sailors killed on board the ships are buried with dignity and respect.

Last month Pollard also urged the House of Commons to take urgent action.

Three British warships, HMS Electra, HMS Encounter and HMS Exeter, all went down in the 1942 Battle of the Java Sea, part of an allied campaign against the Japanese which killed more than 170 British sailors.

The crushing defeat cost the Dutch almost 900 soldiers and led to the Japanese takeover of their colony, the then Dutch East Indies.

It is unclear how many bones the investigative team might uncover, and whether they belonged to Dutch or British sailors, or a combination of both.

In recent years DNA testing of bones matched with the DNA of survivors has proved a successful identification method.