The US will continue to refuse requests for its personnel to appear at inquests into the "friendly fire" deaths of British troops, a report says.
Three UK soldiers died in "friendly fire" in Afghanistan last week
The MoD has sent written guidance to coroners across England and Wales over the holding of military inquests.
According to the Times, its letter says the US "confirms categorically" it will not provide witnesses for inquests.
It comes six days after three British soldiers were killed by US "friendly fire" in southern Afghanistan.
The Times reports that the letter to coroners states: "The US have confirmed categorically that they will not provide witnesses to attend UK inquests.
'FRIENDLY FIRE' DEATHS
Pte Aaron McClure and Pte Robert Foster, both 19, and Pte John Thrumble, 21, killed on 24 August in Helmand
US fighter plane dropped a 500lb (227kg) bomb on their patrol
The only other suspected "friendly fire" death of British service personnel in Afghanistan still under investigation
Since 2001 73 UK troops have been killed on operations in Afghanistan
"While coroners may continue to ask for US witnesses to attend... they should be aware that there will in all cases be a refusal."
The three soldiers who died on Thursday were Privates Aaron McClure and Robert Foster, both 19, and John Thrumble, 21, of the 1st Battalion The Royal Anglian Regiment.
They had been on patrol in Helmand province when US fighter planes dropped a 500lb bomb, killing them and injuring two other soldiers. The US State Department is investigating the deaths.
In March, Oxfordshire assistant deputy coroner Andrew Walker was critical of the failure of the US authorities to co-operate at the inquest of Lance Corporal of Horse Matty Hull.
L/Cpl Hull, 25, died when a US pilot fired on his convoy in Iraq in 2003. No American witnesses gave evidence at the inquest.
L/CPL MATTY HULL
L/Cpl Matty Hull, 25, was killed in Iraq on 28 March 2003, when he came under fire from US A-10 "Tank Buster" plane
Oxfordshire assistant deputy coroner Andrew Walker concluded in March 2007 the attack on Hull's tank was criminal
American authorities criticised for lack of cooperation with inquest
Sun newspaper published a transcript of a cockpit video it obtained of the attack in February
At the start of the attack, pilot notices orange panels on the vehicles
Pilot asks if "friendly" units are in area
He is assured are no coalition forces in area
Pilots open fire but soon the error is realised
The coroner said at the time: "I find the decision of the US authorities not to allow the relevant persons to attend to give evidence, or to themselves provide full transcripts of questions those people were asked during the Friendly Fire Investigation Board, hard to understand."
The Ministry of Defence said the letter to coroners did not mark a change of position.
A spokesman said: "The MoD remains committed to supporting the work of every UK coroner. Indeed the Wiltshire coroner praised the level of support he received from us.
"Both the US and UK work together to investigate the circumstances surrounding friendly fire incidents and their findings are made available to the coroner, as national and operational security and data protection allow.
"The MoD does all that it can to assist the coroner during inquests and liaises with the US government to facilitate requests for information."