KHARTOUM, Dec 30 (Reuters) - Sudanese security forces questioned a veteran opposition leader over comments he made supporting a war crimes case against the country's president, but then released him, state media reported on Tuesday.

The incident was part of a crackdown on Sudanese seen as backing the International Criminal Court and its chief prosecutor, who has asked for an arrest warrant for President Omar Hassan al-Bashir, accusing him of orchestrating genocide in Darfur.

The vice president of the Democratic Unionist Party (DUP), Ali Mahmoud Hassanein, was questioned about "negative remarks he made supporting the ICC allegations against the president of the republic," said the Sudanese Media Centre, a news outlet with links to Sudan's security service.

Hassanein, a lawyer in his 70s, was also asked about consultations he had held with "a senior official in one of the Western embassies known for their continued hostility to the country," the Media Centre said.

Hassanein's supporters said he was arrested at his house on Monday morning and released late that evening.

"He has made a number of speeches saying he supports the International Criminal Court as an institution -- as a human rights institution," said party member and lawyer Muez Hadra.

"He did not say anything about the president's case ... The security officers told him there should not be anyone in Sudan who supports the ICC."

Hadra said the party was preparing an official statement of protest against the arrest.

A security source denied Hassanein had been arrested, telling Reuters he had voluntarily come in for questioning. Hassanein was not immediately available for comment.

Last month, rights groups said three human rights campaigners were arrested and interrogated by security in Khartoum on suspicion of having links with the Hague-based ICC.

A former Sudanese police officer is currently in court, accused of trying to pass sensitive documents to the ICC. Mohamed Alsary Ibrahim has denied the charges.

ICC judges have already issued arrest warrants for a Sudanese minister and a militia leader, accusing them of atrocities in Sudan's western Darfur region. Khartoum has refused to hand them over. (Reporting by Andrew Heavens; editing by Tim Pearce)

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