"Security is our top priority," Modi said in a speech before thousands at the landmark Red Fort in New Delhi as the country marked the 70th anniversary of the end of British colonial rule.
"Be it the sea or the borders, cyber or space -- in all spheres, India is capable and we are strong enough to overcome those who try to act against our country," the Hindu nationalist leader declared.
His remarks came as New Delhi's dispute with Beijing over a strategically key Himalayan plateau enters its second month on Wednesday, with hundreds of soldiers reported to be facing off against each other.
The giant neighbours share a long history of mistrust and went to war in 1962 over the Indian state of Arunachal Pradesh, and are still embroiled in a dispute over the territory.
India is also mired in a border row with Pakistan over the disputed Himalayan region of Kashmir since their bitter split in 1947.
India accuses Pakistan of sending "terrorists" across the border to fight security forces in Indian-administered Kashmir which is divided between the rival neighbours.
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