An Indian woman was gang-raped and then brutally murdered by men who smashed her skull with bricks after she had threatened to inform authorities, police in the northern state of Haryana said on Monday.

Two men were arrested for rape and murder in Sonipat town, and six more were being investigated after the victim's mother accused them of involvement, Ashwin Shenvi, superintendent of police, told the Reuters news agency.

The 23-year old woman, a labourer, was taken by the men - at least one of whom knew her - by car from near her home in Sonipat to the nearby city of Rohtak, where they raped her, Shenvi said.

"When she said to them she would complain, they hammered her skull in with bricks," he said. "The way that they brutalised her is horrific."

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The woman had gone missing on May 9, and her decomposed and mutilated body was found in an open field in Rohtak two days later. Attempts were made to disfigure her completely to prevent identification of the victim, local media said, citing a post-mortem report.

The mother of the victim had previously registered a complaint against one of the accused for pressuring her daughter into marrying him, but the disagreement was settled between the two parties, Shenvi said.

Sonipat is 44km north of India's capital, New Delhi.

Shock and outrage

Sexual violence against women is a highly charged issue in India.

Women's rights activists and politicians have demanded justice for the victim, whose case resembles many aspects of the fatal gang-rape of Jyoti Singh, a student on a bus in New Delhi in 2012.

The case sparked nationwide protests about entrenched violence against women and the failure of authorities to protect them.

"When the accused in Jyoti Singh's case were punished, our village spoke about the verdict. We thought at least this will deter men, but unfortunately even today girls are not safe and men are not scared," the mother of the victim in Sonipat told the NDTV broadcaster.

India has enacted tougher jail sentences for rapists and promised to try those accused through "fast-track" courts but rape, acid attacks and domestic violence remain common.

Haryana Chief Minister Manohar Lal Khattar said that the Rohtak gang-rape case will be heard in a fast-track court, the Hindustan Times reported. Additionally, the Haryana government announced financial assistance of Rs.10.5 lakh [$16,381] for the victim's family.

Opposition leader and Congress Party President Sonia Gandhi expressed deep shock and outrage over the incident, highlighting the need for revisiting the issue of women's safety.

A team by the National Commission for Women, a women's rights group, visited the victim's family in Sonipat, and demanded capital punishment for all those involved in the gang-rape and murder.

Indian media also reported a gang-rape in the city of Gurgaon on the outskirts of Delhi over the weekend.

On average, 50 crimes against women are registered every day by police in Delhi, including at least four cases of rape, according to a senior official in the federal home ministry.