The United States wants China to give a timetable on how it will open up its markets to U.S. exports as the two countries are still "very far apart" on resolving trade frictions, U.S. Ambassador to China Terry Branstad said on Tuesday.

Washington and Beijing have proposed tens of billions of dollars in tariffs in recent weeks, fanning worries of a full-blown trade war that could hurt global supply chains and dent business investment plans.

Earlier this month, a U.S. delegation led by Treasury Secretary Steven Mnuchin presented China with a list of demands to tackle allegations of intellectual property theft and other trade policies Washington considers unfair.

The two countries failed to reach an agreement on the long list of U.S. demands, and decided to resume talks in Washington.

Branstad, who was present at the meeting, said the Chinese appeared to be "taken back" by the significance of the list.

"The Chinese have said 'we want to see the specifics.' We gave them all the specifics in terms of trade issues. So they can't say they don't know what we're asking for," he said.

"We're still very far apart," Branstad said, saying that China has not met pledges to open up its insurance and financial services area, as well as reduce auto tariffs.

"There are many areas where China has promised to do but haven't. We want to see a timetable. We want to see these things happen sooner or later," he said at a conference in Tokyo.

Branstad also said U.S. President Donald Trump would like to see a "dramatic increase" in food exports to China.

"We'd like to see China being just as open as the United States," he said.

The Trump administration has drawn a hard line in trade talks with China, demanding a $200 billion cut in the Chinese trade surplus with the United States, sharply lower tariffs and advanced technology subsidies.

Trump has threatened $150 billion in tariffs on imports of Chinese goods, and China has threatened to retaliate against U.S. exports, including soybeans and aircraft.