Khartoum - A Sudanese judge charged 25 Muslims with apostasy on Thursday after hearing investigators' case against them, which could incur the death penalty if they are convicted.
The men are accused of taking the Qur'an as the sole source of religious legitimacy and rejecting other Islamic texts.
They allegedly belong to a group that adheres strictly to the Qur'an and rejects the authority of the sunnah, traditions attributed to the Muslim Prophet Mohammed.
Both Sunni and Shi'ite Muslims rely on the sunnah as a source of Islamic law.
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Judge Abdallah Abdelbagi said they would be charged for "holding ideas contrary to Islamic beliefs and speaking out about them in public places".
"You have contravened... Article 126 of Sudanese criminal law, under which you will be tried before this court," he added.
Under the Islamic shari'ah law in place since 1983, the group could be sentenced to death if found guilty on Article 126, which deals with apostasy.
The decision came after several hearings in the past two weeks in which investigators presented the charges against 27 men.
At a hearing on Wednesday, the judge dismissed the case against two men who were among the original group arrested earlier this month.
A defence lawyer for the group, Ahmed Ali Ahmed, said the 25 men were not guilty.
"The defendants are not guilty and have not abandoned the Islamic religion," he said told the court on Thursday.
"They are exercising their right to freedom of belief and worship, which is guaranteed under the constitution," he said.
The mostly young defendants were handcuffed throughout the hearing, which took place amid heavy security and riot police guarding the court.
Last week, Ahmed told AFP that 27 men were arrested in the southern Khartoum neighbourhood of Mayo on December 2 and 3.
The trial will resume on Monday, when the defence team will present their case.
After the mostly Christian and animistic south split in 2011, Sudan's population is overwhelmingly Sunni Muslim.