A defence minister has "unreservedly" apologised to those who may have been mistreated by UK forces in Iraq and Afghanistan.
Johnny Mercer's apology comes amid calls for an independent judge-led inquiry to be set up to investigate allegations of abuse and cover-ups by UK special forces.
Mr Mercer, who is Minister for Defence People and Veterans, told MPs there is "no doubt that some of the experiences of those who came into contact with the UK's Armed Forces in Iraq and Afghanistan were completely unacceptable".
He was responding to a Commons debate which highlighted a joint investigation by The Sunday Times and the BBC's Panorama programme into actions by British military personnel during the war on terror.
Scottish National Party defence spokesman Stewart McDonald said the investigators' claims amounted to violations of the Geneva Conventions and that the International Criminal Court should be consulted.
Mr McDonald spoke about the case of a soldier who shot dead four young people in an Afghan village.
He said the case was passed to the service prosecuting authority and a recommendation of war crime charges came forward, before "a cover-up then ensued by military officials".
He claimed there has been "a ruthless and co-ordinated attempt to close down these investigations".
Mr McDonald called on the Government "to be judicious" and approach all allegations with "the seriousness that they deserve".
Responding, Mr Mercer said: "It is a matter of deep personal regret that the original RMP (Royal Military Police) investigations were flawed and that opportunities to hold those responsible to account may now have been lost.
"For this, I unreservedly apologise to those who suffered treatment at the hands of UK forces, that was simply unacceptable.
"And I apologise to our servicemen and women who have, as a result, had years of investigations foisted upon, having more often than not had nothing to do with incidents in questions."
Mr Mercer, a former Army officer, has regularly criticised vexatious historical claims against veterans.
He said there needs to be greater protections for veterans, as well as accountability.
The Ministry of Defence has denied the cover-up allegations.