The Central Bureau of Investigation has started talks with the Portuguese authorities for extradition of underworld don Abu Salem, main accused in the 1993 serial bomb blasts case in Mumbai.

Salem is under judicial custody in Lisbon.

A senior CBI officer, who arrived in Lisbon, handed over the formal extradition request to the Portuguese authorities through the Indian mission there, official sources said.

The CBI has listed Salem's involvement in the Mumbai bomb blasts case and four cases of the Delhi police in its extradition request. The officers also handed over an executive assurance of not sentencing Salem, if convicted, to death.

The Portuguese authorities have already extended the judicial remand of Salem, which was to end on December 16, by three months.

As per the laws in Portugal, no criminal is extradited to any country that awards a death penalty.

The United States has also assured India of its help in extraditing Salem and said that they will "put in a word" with Portugal, its North Atlantic Treaty Organisation ally.

Salem, wanted by India in 71 cases of murder, extortion, forgery, and criminal intimidation, was arrested in Lisbon on September 18 with his girlfriend, Bollywood actress Monica Bedi, following a Red Corner notice issued by the Interpol.