"We will never allow any people, organisation or political party to split any part of Chinese territory out of the country at any time, in any form," Xi said addressing a special ceremony to mark the 90th anniversary of the 2.3 million strong People's Liberation Army (PLA), the world's largest standing army.
Xi's remarks came amid the Sino-India standoff in the Sikkim section.
"The Chinese people love peace. We will never seek aggression or expansion, but we have the confidence to defeat all invasions," Xi, 64, said.
This is the second time in three days that Xi spoke of the PLA's capability to thwart invasions.
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On July 30, Xi during a massive PLA parade had said, "I firmly believe that our gallant military has both confidence and ability to defeat all invading enemies".
Like his earlier address, there was no direct reference in his speech to over a month-long India-China military standoff at Doklam in the Sikkim section.
National Security Advisor Ajit Doval last month during the Brazil, Russia, India, China, South Africa NSAs meet here on July 27-28 also held separate talks with his Chinese counterpart Yang Jiechi.
Both the countries are tight-lipped about the outcome of Doval-Yang talks.