Thousands of Islamist protesters demonstrated in southern Pakistan on Sunday against a new law that reduces the burden of proof on rape victims by allowing them to seek justice without the need for four male witnesses.

The Women Protection Bill, signed into law last month, was seen as a key test for President Pervez Musharraf's philosophy of "enlightened moderation" for his predominantly Muslim country.

The protest in the country's biggest city of Karachi came a day after Musharraf ruled out any changes to the law despite calls from the Islamists.

Some 10,000 supporters of the Islamist parties, most of them bearded, chanted slogans of "Down with Musharraf" and "Down with the Women Protection Law" at the rally and demanded the government scrap the law.

The law takes the crime of rape out of the sphere of the religious laws, known as the Hudood Ordinances, and puts it under the penal code.

Under the Hudood Ordinances, which were introduced by a military ruler in 1979, a rape victim had to produce four male witnesses to prove the crime, or face the possibility of prosecution for adultery.

"We reject this law because it is unIslamic and also against women rights," Fazal-ur-Rehman, a senior leader of the main Islamist alliance and opposition leader in the National Assembly, parliament's lower house, told the rally.

Rehman said the law is a conspiracy to make Pakistan a "free sex zone".

"It is a fight between the liberals and the religious believers... and we will continue our protest against this unIslamic law," he said.

Controversy over the reform of Islamic laws has highlighted a long struggle between progressives and religious conservatives over the direction of Pakistani society.

Women's groups have called for the total repeal of the Islamic laws, which still ban sex outside marriage and stipulate that women adulterers can be stoned to death. But they have hailed the new law, saying it would help mitigate sufferings of thousands of women.