A Chinese soldier stands guard on the Chinese side of the ancient Nathu La border crossing between India and China on July 10, 2008.

China's Foreign Ministry on Thursday said India has been building up troops and repairing roads along its side of the border amid an increasingly tense stand-off in a remote frontier region beside the Himalayan kingdom of Bhutan.

The stand-off on a plateau next to the mountainous Indian state of Sikkim, which borders China, has ratcheted up tension between the neighbours, who share a 3,500-km (2,175-mile) frontier, large parts of which are disputed.

"It has already been more than a month since the incident, and India is still not only illegally remaining on Chinese territory, it is also repairing roads in the rear, stocking up supplies, massing a large number of armed personnel," the foreign ministry said in a statement.

"This is certainly not for peace."

Early in June, according to the Chinese interpretation of events, Indian guards crossed into China's Donglang region and obstructed work on a road on the plateau.

The two sides' troops then confronted each other close to a valley controlled by China that separates India from its close ally, Bhutan, and gives China access to the so-called Chicken's Neck, a thin strip of land connecting India and its remote northeastern regions.