US President-elect Donald Trump is clear about China's position on the Taiwan issue and China has maintained contacts with his team, the foreign ministry says, as Mr Trump took to Twitter to complain about Chinese economic and military policy.
Mr Trump's unusual call with Taiwan President Tsai Ing-wen on Friday prompted a diplomatic protest on Saturday, though US Vice President-elect Mike Pence played down the telephone conversation, saying it was a "courtesy" call, not intended to show a shift in US policy on China.
In Beijing, foreign ministry spokesman Lu Kang would not say directly who China had lodged "stern representations" with about Mr Trump's call, repeating a weekend statement that it had gone to the "relevant side" in the United States.
"The whole world knows about the Chinese government's position on the Taiwan issue. I think President-elect Mr Trump and his team are also clear," Mr Lu told a daily news briefing.
"In fact, China has maintained contacts and communication with the team of President-elect Mr Trump," he added, repeating a previous assertion, though did not give details.
Mr Lu described the matter of Taiwan as the most important and sensitive question between China and the United States.
Mr Trump, who vowed during his campaign to label China a currency manipulator, issued more tough rhetoric on Sunday.
"Did China ask us if it was OK to devalue their currency (making it hard for our companies to compete), heavily tax our products going into their country (the U.S. doesn't tax them) or to build a massive military complex in the middle of the South China Sea? I don't think so!" Mr Trump said on Twitter.
China, Taiwan, the Philippines, Vietnam, Malaysia and Brunei claim parts or all of the energy-rich South China Sea, through which trillions of dollars in trade passes annually.
Mr Lu would not be drawn on directly commenting on Mr Trump's tweets, but defended the China-US relationship.
"The China-US economic and trade relationship has over many years always been a highly mutually beneficial one, otherwise it couldn't have developed the way it has today," he said.
"China and the United States maintaining good relations, a steadily developing relationship, accords with the joint interests of both peoples."
The call with Taipei was the first by a U.S. president-elect or president with a Taiwan leader since President Jimmy Carter switched diplomatic recognition to China from Taiwan in 1979, acknowledging Taiwan as part of "one China". China regards Taiwan as a renegade province.
China blamed Taiwan for the call, but also lodged the diplomatic protest with the United States, saying the "one China" policy was the bedrock of relations with the United States.