The United States said on Sunday it was deeply concerned by reports of viral videos showing two Christian women paraded naked in India's northeastern state of Manipur, a sexual assault case that enraged the country.

The assault, in which a mob allegedly raped and paraded the naked women, took place over two months ago, but it captured national and global attention as the video went viral on social media in the past week.

Police have made some arrests. 

In recent months, hundreds of churches have been burned and thousands of Christians displaced due to ongoing violence between the predominantly Christian Meitei tribe and the mostly Hindu Kuki tribe.

At least 125 people have been killed and more than 40,000 have fled their homes since the violence erupted in Manipur.

A U.S. State Department spokesperson called the incident "brutal" and "terrible" and said the United States conveyed its sympathies to the victims.

The assault was reported by the victims aged 21 and 19 in May during intense ethnic clashes between the tribal Kuki people and majority ethnic Meitei over potential changes to economic benefits.

The trouble was quelled after New Delhi rushed thousands of paramilitary and army troops to the state of 3.2 million people. But sporadic violence and killings resumed soon afterwards and the state has remained tense since.

The United States encouraged a peaceful and inclusive resolution to the Manipur violence and urged authorities to respond to humanitarian needs while protecting all groups, homes and places of worship, the State Department spokesperson said.

Indian Prime Minister Narendra Modi on Thursday condemned the assault as "shameful" and promised tough action.