Scotland Yard is investigating claims that families of members of the armed forces killed in Afghanistan and Iraq have been targeted by Glenn Mulcaire, a private investigator who worked for the News of the World.

The revelation is likely to further shock the public, who have already reacted with horror to news that the paper intercepted voicemails left on a phone belonging to murdered schoolgirl Milly Dowler and targeted the phones of families of victims of the 7/7 attacks.

MPH Solicitors, whose clients include Samantha Roberts, the widow of Sergeant Steven Roberts of the 2nd Royal Tank Regiment, said they had been contacted on Wednesday by a newspaper and told Roberts's phone may have been hacked, along with a mobile belonging to Geraldine McCool, her lawyer.

McCool, a senior lawyer who represented Roberts, said there was no evidence to show confidential information was obtained through hacking.

She added: "Whilst this developing story continues to shock and concern I confirm that I have never seen a news article that gave rise to concern that information had been obtained through illegal phone-hacking.

"I sincerely hope that any future revelations do not involve our clients and that full disclosure of the extent of this diabolical practice is now made."

Sergeant Roberts, from Shipley, West Yorkshire, was accidentally shot dead by one of his own men when UK troops opened fire during a riot near Basra, just three days into the war.

McCool said there was no evidence confidential information had been obtained, saying: "Solicitors are cautious when leaving messages due to client confidentiality and my military clients and their families come from a background that works on a 'need to know' basis."

The News of the World's owner News International said it was contacting the Ministry of Defence to verify the claims. It said in a statement it would be "absolutely appalled and horrified" if they were true.

An MoD spokesman said: "This is a matter for the Metropolitan police who are investigating these allegations.

"It would be inappropriate for us to comment whilst this investigation is ongoing."

Conservative MP Patrick Mercer described the latest phone-hacking allegations as "very damaging".

Mercer, a former infantry officer and journalist, told the BBC that the revelations would add to trauma of the families of dead armed forces members. He said: "The idea that the death of their son or whatever is going to be the subject of a sordid investigation by journalists who are, at the end of the day, hoping to make monetary profit out of it, is deeply unpalatable and will only add to the grief."

• This article was amended on 7 July 2011. The original stated that Scotland Yard had contacted the relatives of Steven Roberts. This has been corrected