South Korean President Moon Jae-in said on Thursday China should do more to rein in North Korea's nuclear program and he would call on President Xi Jinping to 'lift all measures' against South Korean companies taken in retaliation against Seoul's decision to host a U.S. anti-missile defense system.

In an interview with Reuters ahead of his trip to Washington next week for a summit with U.S. President Donald Trump, Moon said 'strong' sanctions should be imposed if North Korea tests an intercontinental ballistic missile (ICBM) or conducts a sixth nuclear test.

North Korea will acquire the technology to deploy a nuclear-tipped ballistic missile capable of hitting the mainland United States "in the not too distant future," Moon said.

"I believe China is making efforts to stop North Korea from making additional provocations, yet there are no tangible results as of yet," Moon told Reuters at the sprawling Blue House presidential compound.

"China is North Korea’s only ally and China is the country that provides most economic assistance to North Korea," Moon said. "Without the assistance of China, sanctions won't be effective at all."

Moon was elected in May pledging to take a more moderate approach to the North and engage the reclusive country in dialogue, in addition to pressure and sanctions to impede its defiant pursuit of nuclear weapons and ballistic missiles.