Roy Keane has assured the Republic of Ireland he is not an "animal" or a "monster" as he responded to criticism from Sir Alex Ferguson and others by condemning the "lies" behind his difficult reputation.

The 42-year-old held his first press conference as the Republic of Ireland assistant manager on Wednesday and was quick to defend himself against allegations he lacks the traits to operate as No2 to Martin O'Neill. Keane was in relaxed, humorous form as he dealt with awkward issues such as his criticism of Irish players following the team's dismal Euro 2012 and O'Neill's weekend admission that the former Manchester United captain was wrong to walk out of Mick McCarthy's squad before the 2002 World Cup. "Martin is entitled to be wrong," he said of Saipan.

He was clearly irked, however, by suggestions his demanding nature may obstruct his return to management and that he would have to rein in the outspoken comments he delivers as a TV pundit. "There's nothing to tame. I'm not some sort of an animal, know what I mean?" Keane said. "I'm a football man and I do push people. I've got that wrong a few times down the years but there were a lot of times when I got it right."

Ferguson was scathing of Keane in his recent autobiography, questioning his former captain's managerial abilities and character as he revealed the extent of the MUTV-inspired fallout that prompted the midfielder's Old Trafford departure in 2005. Keane insisted his official return to the Ireland fold was not the time to elaborate on Ferguson's comments, but promised to do so at a later date.

He said: "I've no issues. The beauty of football is that everybody has opinions and I've no problem with that. The issue I have is when anybody who seems to talk about me, or has issues with what I've said in the past, will just tell lies about me. That's when I'll come out and defend myself. I'm not going to sit here and defend myself regarding Alex Ferguson; that's for another day. I'm not really going to get into that too much. Football is about opinions, no problem about that, but when it's lies that's when you come out and say something. Today is not for that. Today is about talking about getting back involved with the Irish team with Martin, all positive. It's not an area I want to go at today."

Keane also refused to be drawn on Ferguson when asked whether he feared the Scot's influence would damage his career options. "I don't know," was all he would say ahead of, before a lengthy silence. But the former Sunderland and Ipswich Town manager feels his own reputation has counted against him since leaving Portman Road in January 2011. "I have no problems with clubs not giving me an opportunity but I would say that some clubs should certainly have spoken to me over the last year or two," said Keane, who claims to have had two job offers – one from abroad – since leaving Ipswich.

He later elaborated, while admitting O'Neill was one of the few managers in football he could work for: "I'd come across people in football and it would just be a casual thing in my head where I'd go: 'If I had to work with somebody …'People were almost building this monster [saying]: 'I couldn't give him a job.'"

Keane insisted there was no lingering resentment with John Delaney, the chief executive of the Football Association of Ireland, who was prominent in the criticism of the then international captain at the 2002 World Cup. "It was very straightforward," he said of the negotiations with Delaney. "One of my strong points, I hope, and sorry to disappoint, is that when I've had disagreements with people I make up with them and move on very quickly."

The former United captain, though, could not resist a dig at past FAI regimes. He said: "We've had a lovely few days. The hotel is lovely, the food is lovely, the training ground doesn't have any pot-holes. It even has footballs. There's been real progress."

Keane was highly critical of Giovanni Trapattoni's squad after their Euro 2012 flop and has been criticised by Ireland players including Jon Walters, Aiden McGeady and Damien Delaney. He was recently accused of having a "disastrous" relationship with players by Liam Brady, but Keane insists the Ireland squad will discover a softer character than the perceived image.

"Strangely enough I think that will help me with the players if they are thinking one thing and I'm not as bad as everyone makes me out to me in terms of criticising players," he said. "Obviously I'm not going to be the one dropping players or leaving players out and that might give me the opportunity to be nicer to players, but without being a pal to them either. I could be like the nice uncle, but only if we are winning. Everyone has an uncle they don't like, don't they?"