DUBLIN — The police and child protection agencies in Ireland are investigating rape and sexual abuse allegations against more than 30 former members of the Irish Republican Army, based on tips from people who were themselves once linked with the group.

Among those supplying information to the authorities is Gerry Adams, the president of Sinn Fein, an Irish nationalist political party that had close ties to the I.R.A. during the conflict in Northern Ireland. Mr. Adams, who is now a member of the Irish Parliament, confirmed that he had recently passed information to the Irish authorities, and not for the first time.

“I have brought forward information that I have received, and I have no reason to doubt its authenticity,” he said in an interview Monday with the Irish state broadcaster RTE. “It came to me anonymously. It was left in the letter box of my home in Belfast.” He said he would cooperate fully with the police investigation.

Irish news media reports have said that the targets of the investigation were banished from Northern Ireland by the I.R.A. and went to live in the Republic of Ireland. Mr. Adams acknowledged in a blog posting in October that in the years when the group was active in the North, it sometimes shot or expelled people accused of sex crimes.