On Sunday, an 18-year-old woman, who was due to testify in court in October against a man who allegedly raped her in 2011, was shot dead by four assailants on motorbikes in Mau district.
The previous day, a woman aged 22 - who had accused a man of rape in 2013 - was shot dead as she rode on the back of her husband's bicycle in Sitapur district.
Read: Angry mob storms jail to lynch rape accused to death in India
Both victims' families claim the women were being harassed and pressured to withdraw their complaints by the accused, who were out of custody on bail.
Police said they were investigating the murders.
"There must be a formalised protection system in place for victims and witnesses in cases where they are under threat and facing intimidation or worse," said Karuna Nundy, a supreme court lawyer and women's rights activist.
"We also need more and better trained judges and police to deal with these crimes effectively."
Rape victims in India endure an archaic, poorly funded, under-resourced and insensitive criminal justice system, say campaigners.
Read: Four to hang for girl's rape, murder in Indian Kashmir
One of the biggest problems is the length of the trials - sometimes courts can take five to 10 years to reach a judgment. Despite the introduction of fast-track courts for crimes against women, India still has far too few courts, judges and prosecutors for its 1.2 billion people.
Compared to the United States, India has a fifth of the number of judges per capita, and there is a backlog of millions of cases.
Lawyers say victims and their witnesses are sometimes intimidated during lengthy trials by the accused who are, in some cases, granted bail by the court. Some victims can be pressured into accepting illegal out-of-court settlements such as a small cash payment.
Read: Indian man confesses to multiple child murders: police
In more extreme instances, the victim's family is pressured into marrying their daughter to the accused.
Victims face the prospect of spending large amounts of time and money in order to attend multiple court hearings and may become disillusioned with the process.
As a result, cases are often dropped, and the accused acquitted before all the evidence is heard.
Indian police arrest two suspects
Indian police on Monday arrested two men accused of killing their rape victims in target shootings in northern Uttar Pradesh state, officials said.
Assailants over the weekend had shot dead two alleged rape victims in two unrelated incidents in Mau and Sitapur districts in India's most populous state, causing concern over the safety of rape victims.
India recorded 132,000 cases of sexual offences against women in 2014, and some 12,400 occurred in Uttar Pradesh, according to figures from the National Crime Records Bureau.
India introduced tough laws against sex offenders in the wake of the fatal gang-rape of a Delhi student in the capital in December 2012 that sparked mass street protests.
But sexual violence against women has continued at frightening levels throughout the country.
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