Chinese President Xi Jinping meets Ugandan President Yoweri Museveni at the Great Hall of the People in Beijing, China June 25, 2019.

"Regretfully, the U.S. has further increased the tax rate on China's exports to the U.S. This extreme pressure is purely harmful to both sides and not constructive at all," Geng said, according to a CNBC translation.

"I have not heard of this situation regarding the two calls that the U.S. mentioned in the weekend," Chinese Foreign Ministry spokesman Geng Shuang said at press conference on Tuesday. He had denied on Monday that the calls had taken place.

One day later, China is still insisting no phone calls took place over the weekend that President Donald Trump claimed showed its willingness to talk again.

On Monday, Trump said at the G-7 summit in France that China in recent phone conversations expressed its desire for a deal. His comment renewed hopes for a resolution between the world's two largest economies, pushing the market higher as the Dow Jones Industrial Average gained more than 250 points Monday.

Trump abruptly ended the tariff cease-fire earlier this month by slapping more tariffs on Chinese goods, and China retaliated with imposing duties on $75 billion more of U.S. goods and resumed auto tariffs. Trump also said he's ordering U.S. companies to immediately start looking for an alternative to China.

"We hope that the U.S. can maintain calm, return to rationality, stop wrong practices, and create conditions for the two sides to conduct consultations on the basis of mutual respect, equality and mutual benefit," Geng said Tuesday.

Chinese state-run media Xinhua is also sticking to its tough stance on the trade war.

"China did not and will not surrender," Xinhua said in a commentary on Tuesday. "Playing the old tricks of bullying and maximum pressure, the U.S. administration has escalated the trade tensions repeatedly and tried to coerce China into accepting its irrational demands."

Xinhua had called Trump's move to order companies to leave China "ridiculous at best."