China's long process for approving genetically modified crops has become a contentious issue in trade negotiations with the U.S., Reuters reported Thursday, citing two sources with knowledge of the talks.

The Chinese government's process for approving new genetically modified products can take years, which U.S. entities have reportedly said can slow trade.

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Genetically modified crops and the Chinese approval mechanism have been a "big issue," one of the sources told Reuters.

It is one of many issues negotiated between the U.S. and China as the countries work toward a new trade deal. President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE told reporters Thursday that the talks were moving "very well along” and that the countries would eventually reach an agreement.

"They very much want to make a deal," he said. "It has to be a great deal. If it is not a great deal, we’re not doing it."

He added that he expects to announce a trade summit with Chinese President Xi Jinping, but the summit's details were not immediately clear.

Trump last year imposed steep tariffs on China, which responded in kind. The nascent trade war has since been paused with both sides working to reach a deal before it reignites.