BEIJING -- A Chinese official on Friday disputed U.S. President Donald Trump's claim that the deadly opioid fentanyl that is flooding the U.S. is mostly produced in China, just days before a visit by Trump at which he has said he will make China's role in the crisis a major theme of his discussions.

China doesn't deny that some fentanyl produced illicitly inside the country is contributing to the epidemic, Wei Xiaojun, deputy director-general of the Narcotics Control Bureau of the Ministry of Public Security, said at a news conference.

However, according to the intelligence the two countries have exchanged, "the evidence isn't sufficient to say that the majority of fentanyl or other new psychoactive substances come from China," Wei said.

Trump last month said the U.S. was stepping up measures to "hold back the flood of cheap and deadly fentanyl, a synthetic opioid manufactured in China and 50 times stronger than heroin."

He said he would mention it to Chinese President Xi Jinping in Beijing next week. "And he will do something about it," Trump said.

The U.S. Drug Enforcement Administration's representative in Beijing, Lance Ho, declined to comment on Wei's assessment.

However, DEA officials have said in the past that their investigations consistently lead back to China. DEA data also show that when China regulates synthetic drugs, U.S. seizures plunge.

Both the DEA and the White House Office of National Drug Control Policy have pointed to China as North America's main source of fentanyl, related drugs and the chemicals used to make them.

Beijing is concerned enough about international perceptions of China's role in the opioid trade that after The Associated Press published investigations highlighting the easy availability of fentanyl online from Chinese suppliers, the narcotics commission made a rare invitation to a team of AP journalists to discuss the issue at the powerful Ministry of Public Security.

Beijing has long regulated fentanyl and 18 related compounds, and in February also placed carfentanil's less-potent cousins furanyl fentanyl, acryl fentanyl and valeryl fentanyl under control.

Friday's rare news conference was held at the Ministry of Public Security, apparently in a move to emphasize China's progress on co-operation with the U.S. on fighting opioids ahead of Trump's visit.

China, Wei said, has noted Trump's announcement of an opioid crisis and "China attaches great importance to this."

Wei also said the Justice Department's public announcement last month of indictments against two Chinese men accused of making tons of fentanyl and other powerful narcotics sold in the U.S. could impede efforts to bring them to justice.

"I have to admit regret regarding the U.S. move to unilaterally use the method of calling a news conference to announce the matter of these two wanted individuals who've fled to China," he said.

The release of information will "impact on the ongoing joint investigation into the case," Wei said, adding that China noted the U.S. failure to mention their successful co-operation on this and other cases.

The Department of Justice said Xiaobing Yan and Jian Zhang worked separately but similarly and controlled one of the most prolific international drug-trafficking organizations. The lack of an extradition treaty significantly reduces the chances they will be returned to the U.S. for trial.

The Trump administration's anti-drug efforts suffered another recent setback when its nominee for drug czar withdrew from consideration following reports that he played a key role in weakening the federal government's authority to stop companies from distributing opioids.

Trump last week declared opioid abuse a national public health emergency and announced new steps to combat the crisis.

Fentanyl can be lethal even in small amounts and is often laced with other dangerous drugs. The Centers for Disease Control and Prevention estimated the drug and its analogues killed more than 20,000 Americans last year, and the number is rising.