But the Sinn Fein leader said the police and social services also had questions to answer as to how Liam Adams was able to get a job as a youth worker, despite both agencies being aware that his daughter Aine had made claims he raped and molested her.

The republican leader conceded to making mistakes in how he dealt with his brother's situation a day after he revealed that his father, Gerry Adams Snr, had sexually abused a number of his siblings.

Liam Adams, who is currently on the run from police on suspicion of abusing his daughter in the 1970s and 80s, worked in the Clonard Youth Centre in Belfast from 1998 to 2003.

During this period he also worked in the Muirhevnamor Community Youth Project in Dundalk, Co Louth, in the Irish Republic. He was then involved with another youth project in west Belfast from 2004 to 2006.

All three organisations said they were not aware of the claims against Mr Adams. He obtained the positions before vetting checks for people working with children in Northern Ireland became compulsory (the law changed in 2005) and its understood he was not subjected to any such procedure.

Gerry Adams, who first became aware of the allegations against his brother in 1987, said he was not aware he had got a job in the Clonard Youth Centre until he started working there. When he found out, he said he informed the project's organisers of his concerns.

But the management of the centre said they had no record on their files of anybody raising concerns about Liam Adams while he worked there.

While maintaining he contacted the centre, the Sinn Fein president said he could have taken other steps to ensure his brother did not have access to children.

"I'm not above reproach on this and obviously I would handle different issues differently because you learn more and more about how to deal with these issues," he said.