WASHINGTON — President Donald Trump said on Thursday that trade war negotiations with China should wrap up within four weeks and expressed optimism about striking a deal, as top negotiators held new phone talks.

"We are doing very well with China talks," he told reporters. "We are getting what we have to get."

Later, at a Saint Patrick’s Day celebration in the White House with the Irish Prime Minister Leo Varadkar, Trump predicted results in the near future.

"We’ll have news on China probably -- one way or way or the other, we’re going to know over the next three to four weeks," he said.

Top trade negotiators from both sides spoke over the phone on Thursday, according to China’s official Xinhua news agency.

"(Vice premier) Liu He had a third phone call with US Trade Representative Robert Lighthizer and Treasury Secretary Steven Mnuchin, making substantial progress on the (document) text," Xinhua reported.

In Beijing, China’s rubber-stamp parliament approved a foreign investment law that will abolish the forced transfer of technology from foreign firms to local joint-venture partners -- a major sticking point in the trade negotiations.

The law also promises to give foreign firms equal treatment with domestic companies.

Both sides have sent mixed messages over progress of the talks, vacillating between positive assessments and saying more work needs to be done.

The world’s biggest economies continue to lock horns on the hugely complex dispute.

Earlier this week, Trump said there was still no plan for him to hold a summit with Chinese President Xi Jinping.

Trump said on Wednesday he is "in no rush" for a deal but that there is "a very good chance" for one.

Mnuchin told a congressional committee earlier Thursday that he expects the deal to be finalised soon, but cautioned that the process is complex.

"We are working diligently but there are 150-page documents that we are working on," Mnuchin said in response to a question.

The accord will include "very clear enforcement provisions and we want to get the agreement right," he said. "That’s more important that the exact timing."

Trump had said he expected to hold a summit with Xi late this month at his Florida resort.

However, Bloomberg reported that the "signing summit" had been pushed back a month as negotiators struggled to resolve their differences. — AFP