BELFAST -- Gerry Adams, the president of Sinn Fein, the Irish Republican Army's political wing, was an IRA leader in the 1970s and responsible for "many horrendous acts", according to a new book on the Catholic paramilitary organization to be published on Monday.

"A secret history of the IRA," extracts of which were published by the Irish newspaper the Sunday Tribune, deals with the alleged paramilitary career of Adams, one of the artisans of the peace process in Northern Ireland and the IRA's 1997 cease-fire.

"As a leader of Sinn Fein, he denied consistently that he was once a member of the IRA," the Sunday Tribune said.

"Nobody has believed him and there has been a realization that there are understandable tactical reasons for this deception. But it does not mean that everyone should acquiesce with this lie," AFP reported.

Adams rejected the accusations. "Let me once again deny categorically the allegation of my involvement with the IRA, it's not true," he said late Sunday.

The book's author, journalist Ed Moloney, alleged that in April 1971, Adams became commander of the IRA's "second battalion" Belfast, which had 400 members and is blamed for numerous killings.

He also alleged Adams approved a campaign of car-bomb attacks in London in 1973.

Moloney, a former Northern Ireland correspondant for the Sunday Tribune and a respected commentator, accused Adams and his men of responsibility for the kidnapping and "execution" of Jean McConville in 1972, a mother of 10 who was suspected of working as an informer for British agents.

In 1999, Adams asked the IRA to reveal to victims' families where McConville and about 10 others killed by the IRA were buried.

But despite months of searching, their remains have never been found.

The IRA has been blamed for just over half the violence-related deaths in three decades of unrest in Northern Ireland that preceded the 1998 Good Friday peace accord, which brought power-sharing in government for Catholics and Protestants.

Northern Ireland's mainly Catholic Republicans want to reunite the province with the Republic of Ireland, while the unionists -- predominantly Protestant -- want it to remain part of Britain.