Narendra Modi, the leading candidate to be India's next prime minister after a forthcoming election, declared the disputed territory of Arunachal Pradesh an integral part of India on Saturday and urged China to abandon its "mindset of expansion".
India and China fought a brief border war in 1962. The nuclear-armed neighbours signed a pact in October to ensure that differences on their shared border do not spark a confrontation.
"No power on earth can snatch away Arunachal Pradesh," Modi, donning the region's traditional headdress and jacket, was shown on television saying on a campaign stop to the state.
"Times have changed. The world does not welcome the mindset of expansion in today's times. China will also have to leave behind its mindset of expansion."
India regularly holds elections in Arunachal Pradesh, which lies in a remote eastern stretch of the Himalayas and has been administered as part of the Indian state for decades.
China questions India's claim to the territory and calls it South Tibet.
President Pranab Mukherjee described Arunachal Pradesh as an integral part of the country on a visit last November, sparking a heated exchange. China urged India not to aggravate problems on their shared border.
The two Asian giants have a complicated relationship marked by both booming economic ties and growing distrust.
Last May, the two armies were locked in a three-week standoff in the western Himalayas after Chinese troops set up a camp at least 10 km (6 miles) inside territory claimed by India, triggering a public outcry and calls that India should stand up to its powerful neighbour.
Modi's Hindu nationalist Bharatiya Janata Party is the front-runner in a national election due by May.
A three-time chief minister of booming Gujarat state, he has made growth a central plank of his campaign, promising to revive the sagging economy, cut red tape and fight corruption.
But his record as chief minister has been overshadowed by riots 12 years ago in which Hindu mobs killed at least 1,000 people, most of them Muslims. He denies allegations by rights groups that he allowed or encouraged the attacks and a Supreme Court inquiry found no evidence to prosecute him.