An inquiry into the running of a battalion while it was under the command of Colonel Tim Collins has been described as farcical by the father of a soldier who died while serving under him.
Lt Col Tim Collins: Commanded barracks where soldier apparently killed himself
The inquiry announced by the MoD on Friday centres partly on an ongoing inquiry into the apparent suicide of 18-year-old Paul Cochrane at Drumaad barracks in Northern Ireland in 2001.
It will look into issues of the command culture, discipline and could, in theory, trigger another full-blown investigation.
Northern Ireland-born Colonel Collins, 43, was commanding officer of the regiment at the time.
The colonel is also being investigated after allegations were made by an American officer about his treatment of Iraqi civilians and prisoners of war.
The MoD stressed the two inquiries were unrelated and would be conducted separately.
A spokesman said: "We can confirm that a further internal investigation will be conducted to examine the military environment that existed within 1 Royal Irish during the period leading up to Ranger Cochrane's death."
However, the dead soldier's father, Billy Cochrane, said he had no confidence in the inquiry.
"It will be another internal inquiry by officers into officers," he said.
"Nothing will come out of it. It is all farcical."
Mr Cochrane said there was no evidence that the colonel had given his son a difficult time and called for any inquiry to be a public one.
"They have decided to hold an inquiry into Tim Collins after only three days, and yet Paul had been dead nearly two years and they have refused to release one document about him."
An Ulster Unionist MP said he feared the Collins issue may obscure the suicide investigation.
"The Cochrane family are clearly entitled to answers to their very valid questions," said Jeffrey Donaldson.
"I am concerned there are others with an agenda who are perhaps using this situation, using the allegations made by the American officer in Iraq to discredit a man of whom they are quite frankly jealous, to discredit a regiment for whom I think they have other designs."
Colonel Collins, who won wide praise for a rousing speech to his troops on the eve of the fighting, has been accused of breaking the rules of conduct during the conflict in Iraq.
He said he was confident of being cleared by the war conduct investigation, sparked by allegations made by an American officer.
He said he was astonished by the allegations and remained confident his "good name would be
The Iraqi man at the centre of the allegations, Ayoub Yousif Naser, told the Times newspaper he was struck by the colonel and that he and his son were then made to face a wall.
He is reported to have said he heard the officer give the order to fire before he saw other troops approach with bandages to treat their wounds.
Mr Naser, who was a member of Saddam Hussein's Baath Party, has not made any allegations against the colonel.
If found guilty of the allegations Colonel Collins could face disciplinary action or even expulsion from the Army.
Colonel Collins won praise for his speech to the troops from Prince Charles and President George W Bush is understood to have requested a copy for the wall of the Oval Office.