Western reports said British Prime Minister Gordon Brown condemned Shaikh's execution in a statement issued on Tuesday and that Brown had even personally spoken to a senior Chinese leader about the case.

"It would have interfered with China's judicial authority if the senior leader had accepted Brown's request. How could a criminal be exempted from the death penalty only because he was British?" Wang said.

Experts said courts in China had the right to decide whether a psychiatric assessment was necessary.

"The court, based on available evidence, decided not to do the assessment, and it was strictly in line with the law," Wang said.

China's Supreme People's Court on Tuesday issued a statement, saying it had reviewed and approved the death sentence against Akmal Shaikh and there was no reason to cast doubt on Shaikh's mental state.

According to the court, the British embassy in China and a British organization had proposed a psychiatric examination on Shaikh, but the documents they provided could not prove he had mental disorder nor did members of his family have history of mental illness.

Shaikh himself had not provided materials regarding a mental illness. His legal rights and legitimate treatment had been fully granted in custody and trial, the statement said.

Shaikh was sentenced to death in the first instance by the Intermediate People's Court of Urumqi on October 29, 2008, and his final verdict came in October this year after two failed appeals.

Drug-related crimes had been recognized as serious criminal offences in most countries of the world, and China demanded severe punishment for such crimes, the statement said.

In June, eight people convicted of drug production and trafficking were executed in China. Another two men convicted of heading a gang that smuggled drugs from Myanmar into China were executed in May.

Courts across China handled 14,282 drug-related cases from January to May, up 12 percent over the same period last year. In these cases, 6,379 people were convicted and received severe penalties ranging from five years in jail to a death sentence.