The Fermanagh-South Tyrone MLA said people in the party had been working against him over the last number of days and weeks.
He said media sources inside the UUP were hinting at various scenarios, including a leadership challenge or that party colleagues were going to be removed from their positions.
Mr Elliott said: "There was a lot of briefing going against me and obviously it disappointed me, but obviously you can't continue with that level of briefing against you and the media running those levels of stories."
When asked who was briefing against him, he said: "There was obviously details coming out of party meetings, which is unfortunate."
He explained that "some people have tried to have personal grudges against me," before adding:
"They have had personal attacks on me but I'm not going to go down that road."
He said he made the decision "to keep the integrity of the UUP intact" and also "to protect the party."
There comes a time when you have to say: 'Is what I'm doing better for the Ulster Unionist Party or is it better to let someone else take up that mantle?'
Tom Elliott on UTV Live
Mr Elliott took over as leader from Sir Reg Empey in September 2010, after he was voted in ahead of Basil McCrea.
The 14th leader of the party, he has been at the centre of a number of controversies during his tenure - including the moment he branded Sinn Féin supporters "scum" in an outburst during the Assembly election last May.
The party is now set for another leadership contest at its AGM, which will be held on Saturday 31 March.
However, the outgoing leader says he "would not speculate" on who would be taking over his tenure.
"I certainly will not be commenting on who should be the next leader but I can tell you, whoever the next leader is, will have Tom Elliott's support.
"I don't do regrets and I am pleased that I had the opportunity to be leader."
Looking to the future, Mr Elliott said he wanted to see "a stronger Ulster Unionist party."
On Friday, party colleagues and potential candidates remained tight-lipped over the race for a new leader.
Transport Minister Danny Kennedy said: "I am not confirming at this stage, I want to consult with colleagues and friends throughout the party and even outside the party."
South Down MLA John McAllister said it was "a big, big decision" which he had not yet had time to think about, while Strangford MLA Mike Nesbitt: "I'm in listening mode, I said right from the beginning I would serve the party in whatever way they asked and that's still the case."
Doubtless there will be some serious talking between Nesbitt and Kennedy in the coming hours.
UTV's Political Editor Ken Reid
Speaking from Canada, Lagan Valley MLA Basil McCrea said there were "some major issues to be reconciled and consensus has to be formed."
"Depending on upon how that is reached, depends on who is the best person to take the party forward."
Earlier, Mr Elliott told the Impartial Reporter his life has been made difficult by some of his colleagues.
"I blame the continual build-up of collective issues and the small number of individuals who wanted to make life difficult for me," he said in his first interview after his shock announcement.
He added: "There are journalists who are constantly against me and the party. They never have anything positive to say, they just want to pull me down."
However political commentator Alex Kane said he may have fallen victim to listening to too much conflicting advice.
"It doesn't matter which faction the leader comes from, he has to decide what direction he wants to lead the party in," Mr Kane told UTV.
On Friday a party spokesperson said: "The Ulster Unionist Assembly Group has met at Stormont today following last night's decision by Tom Elliot MLA not to seek re-election to the position of Party Leader at the forthcoming AGM.
"At the Group Meeting warm tributes were paid to Tom's personal and leadership qualities and appreciation was expressed regarding the issues he brought forward on behalf of the party.
"Tom has been a tireless worker on behalf of the party, and the Group wanted to place on record its appreciation for the huge contribution he has made as Leader. He will obviously remain a key player in Ulster Unionism as we move forward."
Nominations for the leadership race close next Friday.
"We look forward to a dignified, disciplined process that is respectful of the Party," the UUP spokesperson added.