WASHINGTON (REUTERS) - President Donald Trump said on Tuesday (April 11) he had told China's President Xi Jinping at a summit last week that Beijing would get a better trade deal with Washington if it helped solve the US problem with North Korea.

"I explained to the president of China that a trade deal with the U.S. will be far better for them if they solve the North Korean problem!" Trump, who held talks with Xi in Florida last week, wrote on Twitter.

"North Korea is looking for trouble. If China decides to help, that would be great. If not, we will solve the problem without them!" he added in a second note.

Persuading China to put pressure on its neighbour and ally North Korea to halt its nuclear weapons and ballistic missile development was a key objective for Trump in his first meeting with Xi.

The two leaders agreed to negotiate a 100-day plan aimed at bringing down China's massive trade surplus with the United States, but the two sides offered few details.

China's ambassador to the United Nations, Liu Jieyi, on Tuesday repeated China's call for a return to dialogue with North Korea, and when asked about Trump linking a trade deal to China's help with on North Korea, told Reuters: "We need to look at the situation on the Korean Peninsula as something that we should work together on."

Trump's linkage of trade and North Korea drew criticism from Senator Charles Schumer, the top Senate Democrat, who has sided with Trump in the past on trade. He called on Trump to stick to his campaign vows to take tough action on Chinese trade abuses.

"I think what he's saying is, if they are tough on North Korea, I'll go easier on trade," Schumer said told reporters."Ask the American people if they like that deal. They won't."

A senior administration official, who spoke on condition of anonymity, told Reuters China had suggested some areas where trade frictions could be reduced.

"We are adding some additional items to that list," the official said, while declining to give details.

Opening China to US beef and US services-sector investment are among the topics in the trade talks, White House spokesman Sean Spicer said on Monday.

China agreed last year to end a 13-year ban on US beef, but purchases have yet to resume.

"An absolutely minimum starting point is for China to start honouring agreements it's already committed to," the US official said.