China’s exports to developing markets have soared, opening indirect routes to the U.S. market that officials in Beijing worry may be closed under pressure from President Trump.

Trump cited the fentanyl issue as the reason for imposing a 10% tariff on all Chinese imports in early February, on top of any existing duties. He doubled that to 20% earlier this month. He also has cited fentanyl, along with other reasons, for imposing tariffs on Canada and Mexico.

President Donald Trump’s executive order imposing an across-the-board 10% tariff on all US imports from China went into effect. A month later, he doubled it to 20%.

Walmart is getting caught in the middle of an escalating trade war between the United States and China. Chinese officials confirmed on Thursday they had met with executives from the US retail giant, following a news report that it had pressured its suppliers in China for discounts to cope with rising tariffs imposed by Donald Trump.

The leaders of both Canada and Mexico got on the phone with President Donald Trump this past week to seek solutions after he slapped tariffs on their countries, but China’s president appears unlikely to make a similar call soon.

Officials from China’s Foreign Ministry and the Ministry of Public Security said in a briefing the country has achieved success in controlling the drugs and done all it can for the U.S.

China has taken multiple steps to control the illegal fentanyl trade, responding to concerns raised by the U.S. government. Fentanyl, a powerful synthetic opioid, has been linked to a rising number of overdose deaths in the U.