A couple in north-western India have been arrested for allegedly selling their 7-day-old baby to fund the treatment of a sick older son, police said Friday.

Sandhya Devi, her husband and three others were arrested on Thursday, said YR Phansal, district police official of Sriganganagar, a town in the north of the state of Rajasthan.

The couple said poverty had forced them to give up their newborn to pay for the treatment of their 2-year-old son. They were released on bail.

The baby has been returned to the couple, the police said.

A pregnant Sandhya Devi had been offered 40,000 rupees (about 722 dollars) by a couple who were neighbours if she delivered a boy and gave it to them for adoption, NDTV news channel reported.

"My elder child was sick so I had to give the newborn for adoption for 40,000 rupees, but I only got 20,000 rupees," the father, part-time salesman Ashok Kumar was quoted as saying.

A complaint has been registered against 11 people including the couple who offered to take the baby, the midwife, and officials who allegedly did the adoption paperwork, police said.

Adoptions in India have to be cleared by the government's child protection committees and no money or gifts can be exchanged.

But incidents of destitute women selling their babies illegally are not uncommon in the country.

A woman in the eastern state of Bihar allegedly sold her 8-month-old son in July and her 8-year-old daughter in early August, the Hindustan Times newspaper reported. The suspected trafficker involved in both cases was arrested.

Shantha Sinha, chairman of the National Commission for the Protection of Child Rights, said the incidents were due to the lack of adequate free health care for the poor.

"It is sad that parents are faced with such options and have to make such desperate choices," Sinha said.