Rape cases in New Delhi jumped 23 percent in 2012 from a year earlier, according to official figures, highlighting rising crime against women in the sprawling metropolis.

The numbers were released as the trial of five men was set to begin on Monday on accusations of murder, rape and kidnapping over the death last month of a 23-year-old gang-rape victim, whose assault sparked nationwide protests,

The case against a sixth defendant, who says he is 17, is being heard separately by a juvenile court.

"The rate of conviction in rapes in Delhi is much higher than the national rate," Delhi police Commissioner Neeraj Kumar told reporters on Friday.

"(But) we are not taking solace in this. We need to do much more," said Kumar, who has faced fierce public criticism for the perceived failure of his police force to check mounting crime against women.

For 2012, some 706 rape cases were registered -- a 23.43 percent leap from the previous year, police said.

Some 45 cases of rape and 75 cases of sexual molestation were reported to police in the two weeks after the brutal gang rape attack on the physiotherapy student on December 16, police said.

The victim died in a Singapore hospital from massive internal injuries nearly two weeks after the assault.

New Delhi, a city of 16 million people, has long been called the "rape capital of India".

It is known as the least safe major Indian city for women with more than twice as many rape cases registered in 2011 than commercial hub Mumbai.

Since last month's gang-rape, protesters across India have demanded stronger punishment for crimes against women and better safety.