Key Indian opposition leader Lalu Prasad Yadav was jailed on Saturday (7) for three and a half years over his role in a multi-million dollar corruption case.

Yadav, 69, is a former railways minister and ex-chief minister of the impoverished eastern state of Bihar where he enjoys huge popular support for championing lower castes.

Last month the anti-corruption court found Yadav guilty of fraudulently withdrawing nearly $140,000 from the state treasury in a larger fraud dubbed the "fodder scam", which was worth about 10 billion rupees ($157 million).

Some 60 criminal cases were filed against dozens of politicians and public officials for colluding and defrauding the government in a scheme that was meant to help livestock farmers.

They are accused of inventing vast herds of livestock to obtain public money for fodder and medicines for them.

Yadav denies the allegations, calling them a "political vendetta" by the ruling Bharatiya Janata Party (BJP).

"We are confident that he (Lalu Yadav) will get bail. We have full faith in the judiciary. We are not going to be cowed down," Yadav's son Tej Pratap told reporters after the sentence.

Yadav, a vocal critic of Prime Minister Narendra Modi, was convicted in a first fodder scam case in 2013 and sentenced to five years in jail.

After spending two months in jail, he was granted bail. The conviction means he cannot contest an election and he faces at least one more case.