European leaders sharply condemned the sentencing Tuesday of Burma's most prominent pro-democracy leader to an additional 18 months of house arrest.

British Prime Minister Gordon Brown decried what he called a "sham trial." Sweden, which holds the presidency of the European Union, promised tighter sanctions against Burma's leaders. Amnesty International's secretary general called the verdict "shameful."

Aung San Suu Kyi, head of Burma's National League for Democracy, was found guilty Tuesday of violating the conditions of her house arrest by allowing an uninvited American to stay at her home.

The head of the military-ruled country ordered her to serve an additional 18-month sentence under house arrest. Suu Kyi, a 64-year-old Nobel Peace Prize, laureate has already been in detention for 14 of the last 20 years.

International criticism was swift in coming.

Brown said the verdict showed that Burma's military leaders are "determined to act with total disregard" for international law and opinion.

He called the additional house arrest a "purely political sentence designed to prevent her from taking part in the regime's planned elections next year."

Sweden issued a statement on behalf of the EU saying the verdict continued two decades of violations of international law by Burma's military leadership.

The statement said the EU will respond with "additional targeted measures against those responsible for the verdict (and) will further reinforce its restrictive measures" against Burma's economy.

French President Nicolas Sarkozy was scathing, as well.

"This political trial had just one aim: to prevent Madame Aung San Suu Kyi from leading her fight in favor of a free and democratic Burma," he said in a statement issued in Paris.

Burma, also known as Burma, has been ruled by the military since 1962.

The current junta came to power in 1988 after crushing a pro-democracy uprising. Suu Kyi's party won 392 of 495 parliament seats in 1990 elections, but the military ignored the results. Suu Kyi became a symbol of Burma's suppressed democracy and was awarded the Nobel Peace Prize in 1991.

Irene Khan, Amnesty International's secretary general, said Suu Kyi had faced a maximum sentence of five years.

"The Burma authorities will hope that a sentence that is shorter than the maximum will be seen by the international community as an act of leniency," added Khan. "But it is not, and must not be seen as such."

She said Suu Kyi should never have been arrested in the first place.