An ex-US Marine bomb technician set alight in a barbecue explosion is claiming officials knew about a gas leak which led to the incident.

The 25-year-old has claimed in court documents seen by the ABC that he received 30 per cent burns to his body after attempting to light a barbecue which officials knew had a gas leak.

The documents say that around 11pm on August 1, 2019, Mr Williamson had tried to light the barbecue "to cook some hot dogs and burgers", unaware there was a pre-existing leak.

Barrister for the US government, Dr Christopher Ward SC, argued that the US should "retain foreign sovereign immunity" in the case, as it did not involve any harm or incident to an Australian citizen.