A coroner has called it "inexcusable" that US authorities failed to release evidence about the first UK casualties of the Iraq war.
Andrew Walker was the coroner at the Matty Hull inquest
Andrew Walker was speaking at the reopening of an inquest into the fatal helicopter crash in March 2003.
The eight servicemen died along with four US marines in Kuwait.
American authorities would not give evidence or provide relevant videotape to the court despite all efforts by the MoD, the coroner said.
Mr Walker, Oxfordshire's Assistant Deputy Coroner, criticised US authorities for failing to provide "vital" information during the controversial Matty Hull inquest last month.
In this latest case, Mr Walker told the coroner's court he had been refused permission to use American evidence that would help his inquiry.
Mr Walker said that despite "strenuous attempts by his office and the Ministry of Defence", the US had again said it would not provide any American witnesses to give evidence at his hearing.
"We are again at the beginning of an inquest without the necessary answers to the questions from the US service personnel," he said.
He said the evidence included infrared tape taken by the air mission command aircraft which he believed held radio transmissions before and after the crash.
In addition, footage filmed by an embedded Fox News crew from Fox News was also being withheld, he added.
However, BBC correspondent Jon Brain said the coroner had new information that the images may well be released to the court, after the US authorities had previously denied its existence.
Paul Spencer, on behalf of the family of Sergeant Les Hehir, 34, from Poole, Dorset and the 29 Commando Regiment Royal Artillery, who died in the crash, said widow Sharon Hehir found the US's attitude "inexplicable".
Mr Spencer said: "It's a matter of deep regret and anger on her part that the Americans have refused to cooperate.
"It gives the impression of a cover-up."
The coroner told him: "It seems to me inexcusable that witnesses could come to assist this inquest but they are not allowed to do so."
The Special Investigations Branch military policeman in charge of collecting evidence for the coroner, Warrant Officer 2 Philip Jackson, told the hearing that the Americans' failure to reveal more information was "frustrating to say the least".
He added: "I would like to see more openness in disclosure of the American material."
The British victims were all from 3 Commando Brigade based in Plymouth. The men who died were: Royal Marines Colour Sergeant John Cecil, 35, from Plymouth; Captain Philip Guy, 29, from Bishopdale, North Yorks; Marine Sholto Hedenskog, 26, from Cape Town, South Africa; Warrant Officer 2 Mark Stratford, 39, from Plymouth; and Major Jason Ward, 34, from Torquay.
Also killed were Operator Mechanic (Communications) Second Class Ian Seymour, 29, from Poole in Dorset; Sgt Les Hehir, 34, also from Poole; and Lance Bombardier Llywelyn Evans, 24, of Llandudno, north Wales. Lance Bombardier Evans had a younger brother serving in the same unit.
A British board of inquiry report into the tragedy caused controversy when it differed in the findings of the American report.
The UK inquiry by 3 Commando Brigade found that technical failure was to blame. But British defence chiefs endorsed a US investigation which focused on pilot "disorientation".