Meanwhile, Beijing slams a new US defence act, which includes measures to strengthen Washington's ties with Taiwan and support for Hong Kong's anti-government protestors, saying it "blatantly interfered" in China's internal affairs.
President Donald Trump on Saturday said the United States and China would "very shortly" sign their so-called Phase One trade pact.
"We just achieved a breakthrough on the trade deal and we will be signing it very shortly," Trump said at a Turning Point USA event in Florida.
The Phase One deal was announced earlier this month as part of a bid to end the months-long tit-for-tat trade war between the world's two largest economies, which has roiled markets and hit global growth.
Under the deal, the United States would agree to reduce some tariffs in exchange for a big jump in Chinese purchases of American farm products.
Treasury Secretary Steven Mnuchin said last week the pact would be signed in early January, saying that the deal had already been translated and was just undergoing a technical "scrub."
China says US defence act 'blatantly interfered' in its affairs
Beijing earlier on Saturday slammed a new US defence act, which includes measures to strengthen Washington's ties with Taiwan and support for Hong Kong's pro-democracy protestors, saying it "blatantly interfered" in China's internal affairs.
The tough-worded statement by China's top lawmaking body comes a day after President Xi Jinping told his US counterpart Donald Trump that US comments and actions regarding Taiwan, Hong Kong, Xinjiang and Tibet were harming ties between the two economic giants.
China has recently come under strong criticism in Congress, including from Trump's Republican party, over its attempt to clamp down on anti-Beijing protests in Hong Kong.
There is also growing concern in Washington, among both Democrats and Republicans, over the mass repression of ethnic Uighurs, a mostly Muslim minority in northwest China's Xinjiang region.
The National Defense Authorization Act (NDAA) calls for a report on the treatment of minorities in Xinjiang and to improve military ties with Taiwan, which Beijing regards as a renegade province awaiting reunification, by force if necessary.
You Wenze, a spokesman for the Foreign Affairs Committee of China's National People's Congress (NPC), told state-run Xinhua news agency, that the bill "blatantly interfered" in China's internal affairs.
The parts relating to Taiwan undermined peace and stability across the Taiwan Strait, he said.
Trump signed the $738 billion bill into law on Friday. It also calls for support for Hong Kong's pro-democracy protestors.
Washington's attempts to interfere in other countries' domestic affairs using so-called democracy and human rights would be in vain, You told Xinhua.
He expressed "resolute opposition" to the bill, the Xinhua report said.
The statement echoes the language used during a Xi-Trump phone call on Friday.
"China expresses serious concerns over the US side's recent negative words and actions on issues related to China's Taiwan, Hong Kong, Xinjiang and Tibet," Xi said during the call, according to Xinhua's summary.
Xi "noted that the US behaviours have interfered in China's internal affairs and harmed China's interests, which is detrimental to the mutual trust and bilateral cooperation," the state-controlled outlet said.