Murdered gay rights activist David Kato was mocked at a UN-backed debate on Uganda's anti-homosexuality bill, according to a US diplomat in Kampala in a leaked American embassy cable.

The diplomat said Kato, who was bludgeoned to death near his home in the capital, Kampala, last month, delivered a well-written speech against the bill, but his words were almost inaudible due to "his evident nervousness". Throughout his talk a member of the Ugandan Human Rights Commission "openly joked and snickered" with supporters of the bill, the diplomat claimed in the cable.

The "consultative meeting" in December 2009, organised with funding from the UN, aimed to discuss the bill, which would impose the death penalty for "aggravated homosexuality" and life imprisonment for consenting adults who have gay sex.

In the cable, dated 24 December 2009, the diplomat claimed Ugandan politicians, including the author of the anti-homosexuality bill, David Bahati, had channelled anger at the country's socio-political failings into "violent hatred" of gay people.

Other confidential memos sent between Kampala and Washington in 2009-2010 and sent to WikiLeaks paint a picture of a worsening human rights climate in the runup to Ugandan elections on Friday . They chart Uganda's "chilling" descent from tolerance to violent homophobia and a deepening fear among gay activists, who claim they are being increasingly monitored and harassed.

The memos, classified as confidential, also reveal US diplomatic attempts to combat the draconian bill – which is at the parliamentary committee stage.

Under the heading Comment: Homophobic Demagogues, the diplomat reports in the Christmas Eve cable that Bahati, a born-again Christian MP from the ruling party, had become "further isolated" following "recent condemnations" by high-profile Pastor Rick Warren and other US-based individuals who are against the bill. However, it was clear he would not yield to international pressure.

Referring to Bahati, the diplomat said: "His homophobia … is blinding and incurable."

The diplomat refers also to James Nsaba Buturo, Uganda's minister for ethics and integrity, a strong supporter of the bill, and Pastor Martin Ssempa, who organises anti-gay rallies in Uganda, as key players ushering in a new era of intolerance.

"Bahati, Buturo, and particularly Ssempa's ability to channel popular anger over Uganda's socio-political failings into violent hatred of a previously unpopular but tolerated minority is chilling," the diplomat said.

Kato's murder came three months after Rolling Stone, a Ugandan newspaper, published his name and photograph next to the headline: "Hang them". It attracted worldwide condemnation, with President Obama and the Archbishop of Canterbury, Dr Rowan Williams, calling for a thorough and impartial police investigation.

Ugandan police at first claimed the motive was theft, but have since arrested a suspect. They have now said the killing was the result of a "personal disagreement" unrelated to his activism.

Several of those identified in the Rolling Stone article reported subsequent harassment.

The cable described in detail the Ugandan Human Rights Commission debate on the 18 November 2009, which it said was organised with support from the UN Office of the High Commissioner on Human Rights at which Bahati, Ssempa and Kato, the leader of Sexual Minorities Uganda (SMUG), were all present. Kato left shortly after his speech.

The diplomat said that, prior to the debate, he had received a text message from a gay rights activist expressing concerns for the safety of representatives scheduled to attend.

Bahati led a "tirade against homosexuality" attacking White House opposition to the bill and insisting that impending oil revenue would free Uganda from foreign influence. His message to President Obama was that "homosexuality is … an evil we must fight", which prompted loud applause, led by Ssempa pounding his hand on the table, the cable said.

The UN Office of the High Commissioner for Human Rights has spoken out against Uganda's anti-homosexuality bill, describing it as "draconian" and "unacceptable", and in breach of international human rights standards.

In a later cable, dated 16 February 2010, the diplomat reported concerns from activists that the draft bill was already affecting gay people's lives.

One activist alleged that some gay people had been arrested and detained by authorities and homophobic extremists who were eager to build legal cases in advance of the legislation's ratification, although the claims were contradicted by another activist who said they were not aware of any arrests. The cable noted that international condemnation of the bill had forced Ugandan leaders to reconsider their initial support of Bahati's legislation, but that "Ugandan officials continue to give conflicting assessments of the bill's prognosis".

The cable concluded "even if the draft bill is shelved in the weeks ahead, rampant homophobia in Uganda won't go away".

The cable said that at a meeting between Maria Otero, the US under secretary for democracy and global affairs, and activists in January last year, several human rights defenders outside of the gay community said the bill was one among several growing state limitations of human rights and democratic freedoms in advance of the presidential elections.

Activists were also concerned at government monitoring of electronic communications, saying that they had been forced to switch telephones, restrict emails and resort to switching codewords when arranging meetings to avoid harassment and eavesdropping, the cable said.