The Ministry of Defence is investigating the deaths of two prisoners in Iraq in the fourth separate inquiry into allegations of abuse by British soldiers.
Military police questioned soldiers from the Black Watch after the deaths of the Iraqis on separate days last week.
One man is believed to have been arrested when weapons were found in his room, after British soldiers had tried to arrest his son for alleged rape. The second man is reported to have been a member of the Fedayeen Saddam.
MoD sources said neither man had been mistreated. Investigators are checking whether proper medical procedures were in place. An MoD spokesman said: "Any death in custody is looked into as a matter of course. There is an investigation by the Special Investigation Branch."
The father of an unnamed Black Watch soldier was reported as saying the deaths had been "the talk of the camp. My son phoned me and was very upset." He said it appeared that one of the men "had been roughed up and died in custody. A number of soldiers are extremely upset."
The Black Watch, one of the Army's oldest and most distinguished regiments, was involved in some of the fiercest fighting by British troops in Iraq. Lieutenant-General Jeff Conway, the commander of the US Marine Corps, was so impressed by their performance that he asked the commanding officer, Mark Riddell Webster, to lecture his officers on how Iraqi resistance "crumbled" at Basra.
The investigation comes after Colonel Tim Collins, who commanded the Royal Irish Regiment, was accused by an American reservist of mistreating Iraqis.
A soldier was also arrested after the discovery of photographs allegedly showing Iraqis being "tortured" and two other soldiers were ordered out of Iraq after allegations that Iraqi PoWs were beaten up.