China has accused India of a border incursion between Sikkim and Tibet, according to Reuters, warning the development could "threaten peace".
China has accused India of incursion into its territory between Sikkim and Tibet, in a dispute which has raised tensions between the countries.
The news agency quoted officials as saying that Indian troops had crossed the border, obstructing work on a road on the Chinese side.
Officials said Indian border guards had obstructed "normal activities" on the Chinese side, and called on India to immediately withdrawn them.
Ongoing tensions over the past weeks have already led Beijing to block the border for official pilgrimages.
India also recently accused Chinese troops of incursion on its side.
The border region saw clashes between China and India in 1967.
The area, the Nathu La pass, is used by Indians going for pilgrimages to Hindu and Buddhist sites in Tibet.
A spokesman with China's foreign ministry said Indian border guards "obstructed normal activities" by the Chinese military and demanded that India withdraw immediately.
The region saw clashes between China and India in 1967, and tensions still flare from time to time.
The BBC's South Asia Editor Ethirajan Anbarasan says the latest development "appears to be one of the most serious border escalations between the two Asian giants in recent years".
The BBC's South Asia Editor Ethirajan Anbarasan says the latest development appears to be one of the most serious escalations between the countries in recent years.
The Nathu La pass on the border between Sikkim and Tibet connects India to Hindu and Buddhist sites in the region and is traditionally used by Indians for pilgrimages to those sites.
Reuters cited Chinese officials as warning the development could "threaten peace".
According to Indian media, tensions between the border guards from both sides have been ongoing for the past weeks, with Chinese troops allegedly crossing into Sikkim and destroying two make-shift Indian army bunkers.
China has also accused India of obstructing the building of a road in what it says is its side of the boundary.
The region has continued to be a source of tension between India and China.
There has been no official comment from India on the accusations so far.
China claims the state of Arunachal Pradesh as its own territory and strongly objected to an Indian decision to allow Tibet's spiritual leader, the Dalai Lama to visit.
According to Indian media, there have been tensions between the border guards from both sides in recent weeks, with Chinese troops allegedly crossing into Sikkim and destroying two make-shift Indian army bunkers.
It then renamed six districts in the region, in a move seen as "retaliation".
The tensions have already led Beijing to block official pilgrimages across the boundary.
Beijing also warned that India's inauguration of a bridge connecting Arunachal Pradesh with the north-eastern state of Assam in May, was the "development of military infrastructure in a disputed province".
