"China's position on the China-India boundary question is consistent and clear-cut," said Chinese Foreign Ministry spokesperson Geng Shuang in response to reports that Modi visited the so-called Arunachal Pradesh Thursday.
"The Chinese government has never recognized the so-called Arunachal Pradesh and is firmly opposed to the Indian leader's visit to the disputed area," Geng said.
"We will lodge stern representations with the Indian side," he said.
The spokesperson said that China and India had reached important consensus on properly managing disputes, and the two sides were working to resolve the territorial disputes through negotiation and consultation.
"The Chinese side urges the Indian side to honor its commitment and abide by the relevant consensus, and refrain from taking any action that may complicate the boundary question," Geng said.
He urged India to cherish the hard-won momentum of improvements in bilateral relations and create enabling conditions for the boundary talks and the development of bilateral relations.
The so-called Arunachal Pradesh was established largely on three areas in China's Tibet -- Monyul, Loyul and Lower Tsayul -- which are currently under illegal occupation by India. These three areas, located between the illegal "McMahon Line" and the traditional customary boundary between China and India, have always been Chinese territory.
In 1914, British colonialists secretly instigated the illegal "McMahon Line" in an attempt to incorporate it into India at the above-mentioned three areas of Chinese territory. None of the successive Chinese governments have ever recognized the line.
In February 1987, Indian authorities declared the founding of so-called Arunachal Pradesh.