China has lodged "stern representations" with the North Korean embassy in Beijing over its sixth and most powerful nuclear test, the country's foreign ministry has said.
North Korea is clear about China's opposition to its nuclear tests, ministry spokesman Geng Shuang said, adding that China upholds talks as the means to resolve the Korean peninsula issue.
He went on to say North Korea "must be very clear" UN Security Council resolutions prohibit such activities, and said China hopes all parties, especially North Korea, "exercise restraint and refrain from further escalating tensions."
The North said it tested an advanced hydrogen bomb for a long-range missile on Sunday, prompting a vow of "massive" military response from the United States if either it or its allies were threatened.
A day later, South Korea fired missiles into the sea to simulate an attack on North Korea's main nuclear test site.
The heated words from the United States and the military manoeuvres in South Korea are becoming familiar responses to North Korea's rapid, unchecked pursuit of a viable arsenal of nuclear-tipped missiles that can strike America.
In Seoul, Chang Kyung-soo, an official with South Korea's defence ministry, told MPs it was seeing preparations in the North for an ICBM test.
Mr Chang also said the yield from the latest nuclear detonation appeared to be about 50 kilotons, which would mark a "significant increase" from North Korea's past nuclear tests.
In a series of tweets, US President Donald Trump threatened to halt all trade with countries doing business with North Korea - a warning to China - and faulted South Korea for what he called "talk of appeasement".
In response, Mr Geng, the Chinese foreign ministry spokesman, told reporters in Beijing that China regarded as "unacceptable a situation in which on the one hand we work to resolve this issue peacefully but on the other hand our own interests are subject to sanctions and jeopardised.
"This is neither objective nor fair".
Additional reporting by agencies
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