Britain's prime minister said he was "appalled" at the execution of 53-year old Akmal Shaikh - China's first of a European citizen in nearly 60 years. His government summoned the Chinese ambassador in London to express its anger.
China defended its handling of the case, saying there not been documentary proof Shaikh was mentally ill. Beijing also criticized Gordon Brown's comments, but said it hoped the case would not harm bilateral relations. The Foreign Ministry called on London not to create any "obstacles" to better ties.
Shaikh's daughter Leilla Horsnell was quoted by the BBC and other British media outlets as saying she was "shocked and disappointed that the execution went ahead with no regards to my dad's mental health problems, and I struggle to understand how this is justice."
Shaikh was arrested in 2007 for carrying a suitcase with almost 9 pounds (4 kilograms) of heroin into China on a flight from Tajikistan. He told Chinese officials he didn't know about the drugs and that the suitcase wasn't his, according to Reprieve, a London-based prisoner advocacy group that is helping with his case.
He was convicted in 2008 after a half-hour trial.
He first learned he was about to be executed Monday from his visiting cousins, who made a last-minute plea for his life. They say he is mentally unstable and was lured to China from a life on the street in Poland by men playing on his dreams to record a pop song for world peace.
The press office of the Xinjiang region where Shaikh had been held confirmed the execution in a statement handed to journalists.
In his statement issued by the Foreign Office, Brown said he condemned the execution "in the strongest terms, and am appalled and disappointed that our persistent requests for clemency have not been granted."
"I am particularly concerned that no mental health assessment was undertaken," Brown said.
The Foreign Office said Foreign Minister Ivan Lewis on Tuesday had reiterated to China's ambassador, Fu Ying, statements by Brown and Foreign Secretary David Miliband condemning Shaikh's execution.
Brown had spoken personally to China's prime minister about the case. Miliband had earlier condemned the execution and said there were unanswered questions about the trial - including over whether there was adequate interpretation during the trial.
Chinese Foreign Ministry spokeswoman Jiang Yu responded that drug smuggling was a serious crime.
"We express our strong dissatisfaction and opposition to the British accusation," Jiang told a regularly scheduled news conference in Beijing.
The official Xinhua News Agency quoted China's Supreme Court as saying Tuesday that although officials from the British Embassy and a British aid organization called for a mental health examination for Shaikh, "the documents they provided could not prove he had a mental disorder nor did members of his family have a history of mental disease."
"There is no reason to cast doubt on Akmal Shaikh's mental status," the Supreme Court was quoted as saying.
Xinhua said Shaikh was put to death by lethal injection. China, which executes more people than any other country, is increasingly doing so by lethal injection, although some death sentences are still carried out by a shot in the head.
The Beijing-based lawyer for Shaikh's death sentence review, Zhang Qingsong, said Tuesday he never got to meet with Shaikh despite asking the judge and the detention center for access. He said China's highest court never evaluated Shaikh's mental status.
According to Reprieve, the last European executed in China was Antonio Riva, an Italian pilot who was shot by a firing squad in 1951 after being convicted of involvement in what China said was a plot to assassinate Mao Zedong and other high-ranking communist officials.
"The death of Akmal Shaikh is a sad indictment of today's world, and particularly of China's legal system. ... We at Reprieve are sickened by what we have seen during our work on this case," said Sally Rowen, legal director of Reprieve's death penalty team.
Reprieve issued a statement from Shaikh's family members saying they expressed "their grief at the Chinese decision to refuse mercy."
The statement thanked supporters, including those who attended a vigil for Shaikh outside the Chinese Embassy in London on Monday night, along with members of a Facebook group that drew 5,000 members in just a few days.
The statement asked the media and public to respect the family's privacy as they "come to terms with what has happened to someone they loved."
Gareth Saunders, a British teacher who knew Shaikh in Warsaw, said his friend was cheerful but obviously very mentally ill. He said the last time they met in an underpass, Shaikh said he was traveling to Central Asia but would return in two weeks.
"I tried to contact after two weeks, no reply. That was the last time I tried to contact him," Saunders told The Associated Press.