"The great rejuvenation of the Chinese nation has entered a key phase, and risks and challenges we face are conspicuously increasing," Xi said, according to state news agency Xinhua. "It's unrealistic to always expect easy days and not want to struggle."

He told an event on Wednesday to mark the new semester at the Central Party School, where

cadres are trained,

that: "[We] must not yield an inch on issues of principle, and defend national sovereignty, security and development interests with an unprecedented quality of mind."

His remarks to

hundreds of mid-level cadres

from around the country did not elaborate on the need to struggle but were made amid

growing tension with the United States

on a range of fronts, including geopolitics, the economy and technology.