BEIJING (Reuters) - Chinese police detained 22 ethnic Mongolians after hundreds of them protested against the seizure of land in Inner Mongolia, an overseas rights group said on Tuesday, in the latest case of unrest in the vast and remote northern region.

More than 80 police used "brutal force" on Monday to break up a demonstration by hundreds of Mongolians from Tulee village near the city of Tongliao, the New York-based Southern Mongolian Human Rights Information Centre said.

The disturbance is likely to be another worry for China which already faces unrest among Muslim Uighur ethnic minority people in its far west and among ethnic Tibetans in the southwest.

In Inner Mongolia, five protesters were seriously injured after they gathered to block a bulldozer from a state-backed forestry company from working on their farmland, the rights group said in an emailed statement.

"Police violently beat up the protesters with batons. Some were bleeding, some were beaten down on the ground. Women were pulled by their hair and thrown into police vehicles," the groups cited one of the protesters as saying.

According to the protester, ethnic Mongolians from the area in the eastern part of the region, about 600 km (400 miles) from Beijing, are seeking the return of about 4,000 hectares (10,000 acres) of land they said the forestry company had ceased to manage.

Police in the region reached by telephone said they were unaware of any protest, and a man who answered the phone at the Tongliao public security bureau said offices were closed on Tuesday for a national holiday.

Normally tranquil Inner Mongolia was rocked by protests last year sparked by the death of an ethnic Mongolian herder who was killed by a truck after taking part in protests against pollution caused by a coal mine.

Ethnic Mongolians took to the streets across the region demanding better protection of the environment as well as protection for their rights and traditions. A court last June ordered the execution of a man for murdering the herder.

Ethnic Mongolians, who make up less than 20 percent of the roughly 24 million population of Inner Mongolia, have complained that their traditional grazing lands have been ruined by mining and desertification, and that the government has tried to force them to settle in permanent houses.

(Reporting by Michael Martina; Editing by Ben Blanchard and Robert Birsel)