WASHINGTON (Reuters) - Neither the United States nor China would win a trade war, the Chinese Embassy in Washington said on Monday, after U.S. President-elect Donald Trump threatened to slap an additional 10% tariff on all Chinese imports when he takes office on Jan. 20.

"About the issue of US tariffs on China, China believes that China-US economic and trade cooperation is mutually beneficial in nature," Chinese Embassy Spokesperson Liu Pengyu said in a statement.

"No one will win a trade war or a tariff war," Liu said.

Trump said he would impose the tariffs until China stops the flow of illegal drugs, particularly fentanyl, into the United States.

In the statement, Liu said China had taken steps to combat drug trafficking after an agreement was reached last year between President Joe Biden and Chinese President Xi Jinping.

"The Chinese side has notified the US side of the progress made in US-related law enforcement operations against narcotics," Liu said.

"All these prove that the idea of China knowingly allowing fentanyl precursors to flow into the United States runs completely counter to facts and reality," Liu said.

There has been incremental but visible progress in co-operation over shutting down illicit traffic in chemicals used to produce deadly fentanyl after Xi and Biden agreed to resume joint efforts last year.

The United States, where fentanyl abuse has been a major cause of death, has pushed China for tougher law enforcement, including tackling illicit finance and clamping further controls on the chemicals.

In June, China's top prosecutor urged its law enforcement officials to focus on combating drug trafficking, as Beijing and Washington unveiled a rare joint investigation into drugs.

In August, days after a meeting of a joint counternarcotics working group, China said it would tighten controls on three chemicals essential for making fentanyl.