GINCHI, Ethiopia — In a grassy field, a group of would-be 12th graders kills time under the midday sun.

No one is going to school anymore, out of fear. In a town crawling with federal and local police officers, even talking in a large group can be dangerous, the young men say.

Seven months ago, protests erupted here in Oromia, a vast region in central Ethiopia that surrounds the capital, Addis Ababa, on all sides.

Since then, more than 400 people have died, with thousands wounded and tens of thousands arrested in a campaign marked by the “lethal force” of the Ethiopian security forces, according to a new report by Human Rights Watch. Nearly all of those killed were civilians, it found.

“Many of those interviewed for this report described the scale of the crackdown as unprecedented in their communities,” the group said.

Getachew Reda, an Ethiopian government spokesman, called the figures baseless but acknowledged that scores of lives had been lost.

“The government regrets the fact that people were killed, because these were avoidable deaths,” he said. “But we believe in many parts of Oromia region, where the protests were quite common, security forces conducted themselves in a very professional and responsible manner.”

Ethiopia has claimed double-digit economic growth rates over the past decade. But the demonstrators argue that members of the Oromo ethnic group, Ethiopia’s largest, were increasingly marginalized as the government displaced small farmers, suppressed local languages and leased communal land to outside investors — all in pursuit of its singular vision for state-led development.

“Our rights were being abused, and we are the owners of this region,” said L.B., 20, a student in Ginchi who would not give his full name for fear of reprisal by the government. “We are only demanding our rights.”

Tensions between Oromia residents and the federal government are not new to Ethiopia, Africa’s second-most populous country. But this outbreak of violence is particularly bad. Demonstrations have erupted in cities and small towns across the region, and security agents stand accused of responding with reckless, often fatal violence.

It all started here in Ginchi last November, when, citizens say, the government sought to clear space for foreign investors by cutting down trees in a nearby forest and taking over a patch of land that children used to play soccer.

When local high school students protested in the streets, L.B. and his classmates said, police officers responded quickly with gunshots, tear gas and arrests. Demonstrations spread quickly to the nearby city of Ambo, and then across the region. They continued in Ginchi, too, where students gathered in December to march in the streets once again.

That time, the young men said, security agents shot indiscriminately into the crowd, hitting three men. One got a bullet to the hip, they said. Another was wounded in the arm. And their classmate Aschalew Warku, 20, was shot in the head.

In the Human Rights Watch report, Mr. Aschalew is No. 75 on a list of 314 fatalities across the region over the last seven months. Dozens of unnamed others have died in the unrest as well, the report estimates.

The government spokesman, Mr. Getachew, countered with numbers from the Ethiopian Human Rights Commission, which reported this month that 173 people had died during the Oromia protests and concluded that the police had responded proportionally.

Felix Horne, the researcher who wrote the Human Rights Watch report, voiced “serious concerns” about the commission’s impartiality.

“To suggest that the shooting of protesters was a proportionate use of force seriously undermines their credibility as an independent institution,” he said.

The protesters have seen at least one of their demands met. A so-called master plan to link Addis Ababa with neighboring towns in Oromia, which protesters saw as an incursion into Oromo territory, was canceled in January. The government has also met with residents and leaders to discuss their concerns.

But many activists say that their ultimate goals, which now include justice in the wake of brutal clampdowns, have not been achieved.

In Shashemene, a town in central Oromia, a 17-year-old student who asked to be identified only by his first initial, M., said that what had begun as a movement for basic rights had been reduced to a struggle to escape persecution by Ethiopia’s security agents.

“They are eager to traumatize us and kill us, and we don’t know how to overcome that,” he said, adding that he had lost two family members in the unrest and had been injured twice by baton-wielding police officers.

Protesting now, he said, would be too risky.

The young men who live in Ginchi feel the same, L.B. said.

“These protests brought the end of the master plan, and we stopped them from cutting down trees in our forest,” he said. “But that doesn’t change the fact that people are still getting arrested all the time.”