(CNN) -- The British government condemned China's execution of a British national Tuesday on drug smuggling charges.

"I ... am appalled and disappointed that our persistent requests for clemency have not been granted," Prime Minister Gordon Brown said. "I am particularly concerned that no mental health assessment was undertaken."

Akmal Shaikh was convicted of carrying up to 4 kilograms (8.8 pounds) of heroin at the Urumqi Airport in September 2007. According to Chinese law, 50 grams (1.76 ounces) is the threshold for the death penalty.

China defended the execution in a statement issued by the Chinese Embassy in London.

"Drug trafficking is a grave crime worldwide," the statement said. "The concerns of the British side have been duly noted and taken into consideration by the Chinese judicial authorities in the legal process, and Mr. Shaikh's rights and interests under Chinese law are properly respected and guaranteed."

The 53-year-old is the first European executed in China in 50 years, according to the British legal group Reprieve.

The Chinese ambassador to the UK, Fu Ying, was summoned to the British Foreign Office in the hours following Shaikh's execution, the Foreign Office told CNN. The ambassador was set to meet Ivan Lewis, minister of state.

"I had a difficult conversation with the Chinese ambassador today," Lewis said in a statement following the meeting. "I made clear that the execution of Mr. Shaikh was totally unacceptable and that China had failed in its basic human rights responsibilities in this case, in particular that China's court had not considered the representations made about Mr. Shaikh's mental condition."

"We are deeply saddened, stunned and disappointed at the news of the execution of our beloved cousin, Akmal," Soohail and Nasir Shaikh said in a statement issued on behalf of the family. "This was carried out this morning despite repeated requests for clemency and a proper appraisal of Akmal's mental state."

His family and the British government had asked Chinese leaders for clemency. His supporters argued that Shaikh was mentally ill, and that Chinese officials did not take his mental condition into account when trying him. Shaikh's advocates say he suffered from a bipolar disorder and that he was tricked into carrying heroin into China with promises of a career as a pop singer.

"The European Union condemns in the strongest terms the execution of Akmal Shaikh," the EU presidency said in a statement. "It deeply regrets the fact that China has not heeded the repeated calls by the European Union and one of its member states for the death sentence passed against Mr. Shaikh to be commuted."

The EU remains opposed to capital punishment, the statement said.

Brown raised Shaikh's case with Chinese Premier Wen Jiabao during the international climate summit in Denmark earlier this month.

British Foreign Secretary David Miliband echoed Gordon Brown's concerns about the execution.

"The UK is completely opposed to the use of the death penalty in all circumstances," Miliband said. "However, I also deeply regret the fact that our specific concerns about the individual in this case were not taken into consideration. ... These included mental health issues, and inadequate professional interpretation during the trial."