India's Supreme Court has stayed the execution of two of four men as they appeal against their sentence for the fatal gang-rape of a student in New Delhi, an attack that shocked the country and sparked weeks of protests.

The court on Saturday suspended the execution of the two men, Mukesh Singh and Pawan Gupta, while an appeal is heard and asked authorities to "communicate the order to prison authorities".

The court held an emergency weekend sitting to hear the motion for the stay of execution. It was not immediately known when the executions had been due to be carried out.

The two, Gupta and Singh, appealed to the Supreme Court after the High Court upheld earlier in the week the death penalty given to the four men convicted of the gang-rape last September.

Last Thursday, the Delhi High Court upheld the four men's sentences in the death of the 23-year-old physiotherapy student, saying the case fell in the "rarest of rare category" under which India carries out executions.

The Supreme Court was told that the other two men convicted of the crime, Vinay Sharma and Akshay Thakur, had not approached the top court to appeal against the High Court ruling.

A fifth suspect had been discovered dead in his jail cell, in what authorities said was a suspected suicide.

The sixth member of the group, a juvenile at the time of the crime, is serving a three-year sentence.