Bollywood actor Sanjay Dutt will have to undergo a jail term of more than three years after the Supreme Court today upheld his conviction in the 1993 Mumbai serial blasts case which it said was organised by underworld don Dawood Ibrahim and others with the involvement of Pakistan's ISI.

However, the apex court reduced to five years the six year jail term awarded to him by a designated TADA court in 2006, ruling out his release on probation because the "nature" of his offence was "serious".

53-year-old Dutt, son of famous bollywood couple late Sunil Dutt and Nargis, has already spent one and half years in jail and was out on bail. Sunil Dutt was a long standing Congressman and was a Union Minister.

Dutt was convicted by the TADA court for illegal possession a 9 mm Pistol and a AK-56 rifle which was part of the consignment of weapons and explosives brought to India for the coordinated serial blasts that killed 257 people and injured over 700.

Bringing to a closure the appeals by the convicts and the state in the case, a bench of justices P Sathasivam and B S Chauhan upheld the death sentence of Yakub Abdul Razak Memon, brother of one of the absconding main conspirators Tiger Memon and life sentences of 16 of the 18 convicts.

The death sentence of 10 others was commuted to life sentence by the court which directed that they will remain in prison till death.

The life sentence of one Ashrafur Rehman Azimulla was reduced to 10 years while Imtiyaz Yunusmiya Ghavte was set free by reducing the sentence to jail term already undergone.

"The circumstances and the nature of the offence is so serious that we are of the view that he (Sanjay Dutt) cannot take the benefit of provisions of the Probation of Offenders Act to release him on probation," the bench said.

"We reduce the punishment of six years to minimum of five years under the Arms Act," the bench said and directed him to surrender within four weeks. .