President Donald Trump speaks while meeting with China's Vice Premier Liu He in the Oval Office of the White House in Washington, U.S., April 4, 2019.

Ahead of a Thursday meeting with Liu, Trump told reporters that "intellectual property and theft" and "certain tariffs" — two of the key topics in the talks — are some of the remaining sticking points.

A Chinese delegation led by Vice Premier Liu He met with U.S. officials Wednesday and Thursday as the two sides try to strike an agreement and end a potentially devastating trade conflict. While the Trump administration has shown optimism about inking a trade overhaul long sought by the president, negotiators still have some differences.

The U.S. and China moved closer to a trade deal during talks this week, but negotiators still need to hammer out some sticking points as they push for a final summit between President Donald Trump and Chinese President Xi Jinping.

"If we have a deal, there will be a summit. I'd say we'll know over the next four weeks," the president said.

The two sides were going line by line through deal text Thursday, with a break for a meeting between Trump and Liu, an administration official told CNBC. They will continue to work through the deal on Friday.

The world's two largest economies still disagree over whether the U.S. will use tariffs as an enforcement tool, the official acknowledged. Trump has previously said his administration's tariffs on $250 billion in Chinese goods could stay in place even after the sides strike a deal. China has pushed for the removal of duties as part of an agreement.

The U.S. and China had not set a date or place for a summit between Trump and Xi as of Thursday.

The talks come as investors and businesses watch closely for developments that could ease tensions between the U.S. and its largest trading partner. The escalating series of tariffs imposed by both China and the U.S. has rattled financial markets and led to concerns about issues rippling throughout both economies.

Trump, who won the White House partly on his pledges to crack down on what he called Chinese trade abuses, seeks a victory that he can promote during his 2020 reelection bid.

"If it's not a great deal, we're not doing it," he told reporters at the White House earlier Thursday. "But it's going very well."

The two sides are eyeing a series of agreements on different subjects tied together by one enforcement tool, the administration official said. The U.S. and China have not decided how much of the agreement to finish now and how much to leave for the potential meeting between Trump and Xi.

The U.S. would give China until 2025 to follow through on commitments to purchase more goods from the U.S., the person added. But different products would be subject to separate timelines. Trump has long decried the trade deficit between the U.S. and China and pushed for Beijing to buy more American goods.

Negotiators have not set a time frame for addressing structural issues, such as stopping intellectual property theft or forced technology transfers.

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