The families of the two girls, who were found dead in a field in Unnao's Baburaha village, on Thursday demanded a CBI probe into the incident.
Three girls, aged 13, 16 and 17, were found unconscious in the field on Wednesday night and two of them were declared brought dead at the hospital. The third girl is undergoing treatment in Kanpur and is said to be critical.
All three belong to Dalit families.
A three-member panel of doctors has been set up to supervise the post mortem.
Meanwhile, Congress MP Rahul Gandhi and party General Secretary Priyanka Gandhi Vadra have tweeted about the incident.
Rahul said women in UP not only Dalits are facing a violation of human rights. "The Congress party will fight to ensure justice for such victims," he tweeted in Hindi.
Priyanka said in a Facebook post that the incident was 'heart-wrenching'.
She asked the state government to shift the third girl to Delhi for advanced treatment and ensure justice for the families.
Priyanka said that according to reports, the families were 'under house arrest' which is unacceptable.
Meanwhile, the Baburaha village where the incident took place, is seeing a heavy deployment of police.
According to the police, the three girls had gone to their fields to cut grass on Wednesday afternoon. When they did not return till late evening, their family members went out to search for them and found them lying unconscious in the field.
The hands and feet of the girls were tied with their dupatta and they were frothing at the mouth, indicating that they had been given poison.
Their clothes, however, were intact.
The brother of the 16-year-old girl, in his statement to the police, said "I spotted my sister along with my two other cousins with their hands and legs tied."
Superintendent of Police, Unnao, Anand Kulkarni, told reporters that the three girls are cousins. "A white substance was oozing out of their mouths, and was visible, when the police teams reached there," he said.
The two bodies have been sent for post mortem.
Family members have alleged murder. "Why would the girls tie their own hands and feet if they were committing suicide? It is a clear case of murder," said a family member.
Samajwadi Party MLC Sunil Singh Sajan, meanwhile, alleged that the Unnao police was trying to hush up the case. He has sought a probe by an independent agency in the matter.
"The incident proves that our daughters are not safe in this regime. Unnao, in the past three years, has witnessed a spate of similar incidents which is a matter of concern," he said.
( With inputs from IANS )
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