Woman journalist Lubna Ahmed Hussein was freed on Tuesday after spending a day in jail for refusing to pay a fine for wearing "indecent" trousers, the Sudanese Union of Journalists said.

"She came out of prison. We paid the 500-pound (200-dollar) fine," Mohedinne Titawi, president of the union, said.

Hussein was imprisoned on Monday after she refused to pay the fine imposed earlier the same day by a Khartoum court for wearing trousers deemed indecent. She could have faced one month in jail.

The journalist was wearing slacks when she was arrested along with 12 other women in a Khartoum restaurant in July.

Sudanese law in the conservative Muslim north stipulates a maximum of 40 lashes for wearing indecent clothing.

Ten of the women were arrested with her were summoned by police and flogged.

Hussein led a public battle against the law, resigning from the United Nations, where she worked as a media officer, to stand trial.

Her case led to an outcry abroad and demonstrations at home.