The execution of four men convicted of the brutal gang-rape and murder of a student on a New Delhi bus in 2012 was indefinitely postponed by a court Monday.

The special court last month ruled the men were to be hanged Tuesday, but postponed the execution after one of them filed a mercy plea -- the last remedy for death row convicts in India -- to the president.

"The execution has been deferred till further notice," defence lawyer A.P. Singh told reporters outside the court in the capital.

Six people -- five men and one juvenile -- were charged with the attack on Jyoti Singh in a case that made headlines around the world and triggered massive nationwide protests.

One of the men, the suspected ringleader, allegedly committed suicide in his prison cell, while four others were convicted in 2013.

The juvenile was released after spending three years in a detention centre.

The Supreme Court upheld death sentences against the four men in 2017 and since then their executions have been stuck in a legal quagmire.

The hangings were initially due to be carried in January, but were postponed because some of the men still had legal options to appeal.

Monday's deferment was the third by the court.

"It's no one's fault. These are legal procedures," the victim's father Badrinath Singh said Monday.

"I am hopeful the next date will be final."