Image caption Gu Kailai: "A tragedy happened because of me"

Gu Kailai has admitted murdering British businessman Neil Heywood and blamed her actions on a mental breakdown, Chinese state media report.

The state news agency Xinhua said the wife of former top politician Bo Xilai had apologised for what she described as the "tragedy" of Mr Heywood's death.

She said she would "accept and calmly face any sentence", the agency added.

Ms Gu was accused of poisoning Mr Heywood with cyanide last November, at her one-day trial on Thursday.

Her aide, Zhang Xiaojun, also admitted his involvement in the murder and said he wanted to apologise to Mr Heywood's relatives, Xinhua reported in a detailed account of Thursday's proceedings in court.

The prosecution alleged Ms Gu and her son, Bo Guagua, had fallen out with Mr Heywood over business interests, and Ms Gu had feared Mr Heywood was threatening her son.

A study commissioned by the prosecution of Ms Gu's mental health found she had been treated in the past for "chronic insomnia, anxiety and depression, and paranoia", and had received medication including anti-psychotic drugs.

She had, the prosecution said, suffered from mental disorders because of a physical and psychological dependence on sedatives.

She and Mr Zhang face the death penalty if convicted, but observers say the suggestion that Ms Gu was protecting her son could be used as a justification for a degree of leniency.

'Fight to the death'

According to the prosecution, Ms Gu arranged to meet Mr Heywood in Novermber 2011 at the Nanshan Lijing Holiday Hotel, where they drank tea and alcoholic drinks. Mr Zhang was also present.

Image caption Zhang Xiaojun also wanted to apologise, Xinhua said

"After Heywood became intoxicated, vomited and asked for a drink of water, she poured a poison into his mouth that had been prepared beforehand and that she had given to Zhang Xiaojun to bring along, causing Heywood's death," a court statement read.

According to testimony attributed to Ms Gu, she said she had believed her son to be in danger.

"To me, that was more than a threat," she was quoted as saying. "It was real action that was taking place. I must fight to my death to stop the craziness of Neil Heywood."

"I suffered a nervous breakdown," she said. "A tragedy happened because of me."

Four senior police officers have admitted charges of covering up evidence linking Ms Gu to the murder, a court official said.

They include Guo Weiguo, former deputy chief of Chongqing's Public Security Bureau, and Li Yang, former chief of the bureau's criminal section.

Court officials did not specify why the officers had sought to cover up the murder and made no mention of Mr Bo, the Reuters news agency reported.

The dates for the verdicts in both trials are yet to be announced.

'Disciplinary violations'

TIMELINE: BO XILAI SCANDAL 6 Feb: Chongqing police chief Wang Lijun flees to the US consulate in Chengdu

Chongqing police chief Wang Lijun flees to the US consulate in Chengdu 15 Mar: Bo Xilai is removed from his post in Chongqing

Bo Xilai is removed from his post in Chongqing 20 Mar: Rumours suggest Mr Bo could be linked to the death of British businessman Neil Heywood

Rumours suggest Mr Bo could be linked to the death of British businessman Neil Heywood 10 Apr: Bo Xilai is suspended from party posts and his wife, Gu Kailai, is investigated over Mr Heywood's death

Bo Xilai is suspended from party posts and his wife, Gu Kailai, is investigated over Mr Heywood's death 26 July: Gu Kailai and Bo family employee Zhang Xiaojun are charged with killing Mr Heywood

Gu Kailai and Bo family employee Zhang Xiaojun are charged with killing Mr Heywood 9 Aug: Gu Kailai goes on trial for murder Bo Xilai scandal: Timeline

The case appears to have ended the career of high-flying politician Bo Xilai, who had been seen as a strong contender for one of China's top jobs, as the country prepares to install a new generation of leaders.

Seven members of the nine-strong politburo Standing Committee are due to retire soon.

Mr Bo was the Communist party head in the city of Chongqing when Mr Heywood's body was found at a hotel in November 2011.

At the time the death was recorded as a heart attack. But four months later Mr Bo's right-hand man, police chief Wang Lijun, fled to a US consulate to allege murder and a massive cover-up.

Media reports said Mr Wang had since been detained and could be put on trial as early as next week.

Mr Bo was sacked in March and is currently under investigation for unspecified "disciplinary violations".