The Supreme Court on Thursday directed preliminary investigation by the Central Bureau of Investigation into allegation that Uttar Pradesh Chief Minister Mulayam Singh Yadav and his family members have amassed wealth disproportionate to their known sources of income.

Besides the chief minister, the court directed probe against his parliamentarian son Akhilesh Yadav, his wife Dimple and other son Prateek.

A bench headed by Justice A R Lakshmanan said that the CBI will scrutinize the documents and decide if a case is made out against them or not.

"The allegation is made against the chief minister of a big state, which has cast cloud on his integrity. Hence, it is in his interest and also to hold public morality in high offices that an independent agency should look into it," the bench said.

Observing that the order was in public interest, the bench said, "The chief minister should not function under a cloud and he should have his honour vindicated."

The direction came on a plea filed by Vishwanath Chaturvedi, a UP resident, who had alleged that the chief minister and his family members had amassed wealth by illegal means during 2001-05.

However, Yadav had alleged that Chaturvedi was a Congress leader and that the public interest litigation was politically motivated. He claimed that Chaturvedi was the head of the PIL cell of Congress and had contested the last assembly elections against BJP president Rajnath Singh.

Chaturvedi had maintained that he was not guided by political considerations to file the PIL against Yadav.