Ethiopian security forces are carrying out a brutal crackdown on peaceful protests in the country's Oromia region and thousands of people are being held without charge, a human rights group has said.

The demonstrations began in November due to a government plan to expand the boundaries of Addis Ababa into Oromia, which surrounds the capital, raising fears among Oromo people that their farms would be expropriated.

Addis Ababa, which has accused the protesters of having links with "terror groups", dropped the plan on January 12 and announced the situation in Oromia was largely under control.

The New York-based Human Rights Watch (HRW), however, said the protests were continuing.

Ethiopia's information minister, Getachew Reda, told Al Jazeera that he had not yet read the report and so could not comment on it.

HRW noted that researchers were unable to determine how many people have been killed or arrested because access to Oromia is restricted.

"[Ethiopian] activists allege that more than 200 people have been killed since November 12, 2015," the rights group said.

In a previous document at the beginning of January, HRW reported at least 140 killings.

"Flooding Oromia with federal security forces shows the authorities' broad disregard for peaceful protest by students, farmers, and other dissenters," Leslie Lefkow, deputy Africa director at Human Rights Watch, said on Monday.

"The government needs to rein in the security forces, free anyone being held wrongfully, and hold accountable soldiers and police who used excessive force," Lefkow added.

The rights group called on the Ethiopian government to end excessive use of force by its security forces, free everyone detained arbitrarily, and conduct an independent investigation into killings and other security force abuses.

The Oromos are the largest ethnic group in the horn of Africa country.