Former US evangelical leader Ted Haggard has admitted to being guilty of "sexual immorality", after he was fired from his position as head of New Life Church in the USA.

The scandal has been hugely embarrassing for those connected with Haggard, particularly as it comes ahead of a key vote on Tuesday to decide if same-sex marriages should be allowed in the state of Colorado.

The disgraced church leader has admitted in a letter one day after being fired: "I am a deceiver and a liar".

In the build-up to Tuesday's vote, and while the issue has been a hot topic across the US, Haggard has been a prominent opponent of gay marriage.

He has now admitted to buying drugs, as well as having a massage from a gay masseur. However, he has adamantly denied using the methamphetamine or having sex with the man.

In the letter that was read out to New Life Church followers in Colorado Springs, Haggard said: "I am so sorry for the circumstances that have caused shame and embarrassment for all of you."

"There is a part of my life that is so repulsive and dark and I've been warring against it my entire adult life."

The furor became public last week, when Mike Jones told a Colorado radio station that he had been paid to have sex with Haggard nearly every month over the past three years.

Haggard denied the accusations but said he did receive a massage from the man after being referred to the masseur by a Denver hotel.

Haggard resigned as the head of the 30m-strong National Association of Evangelicals (NAE) on Thursday over the matter.

Haggard, 50, who has five children and is known to have close contacts with the White House, has also admitted that he bought methamphetamine but "never used it".