Human Rights Watch says Ethiopian security forces have killed more than 400 people in a crackdown on protests in the Oromia region since November.

The rights group said in a report released Thursday that tens of thousands of others have been arrested.

It urged Ethiopian authorities to urgently support an independent investigation into the killings and other abuses.

There was no immediate comment from the Ethiopian government.

The student-led protests were sparked by a government plan to expand the municipal boundaries of the capital, Addis Ababa, into Oromia, where farmers fear they will lose their land.

The proposal has since been retracted.

Ethiopia's government frequently faces allegations of rights abuses against opposition groups, journalists and minority groups.