Top trade negotiators from China and the United States (US) held a phone call on Tuesday morning, China's Commerce Ministry said, as the two sides try to hammer out a preliminary “phase one” deal in a trade war that has dragged on for 16 months.

Chinese Vice Premier Liu He spoke with US Trade representative Robert Lighthizer and US Treasury Secretary Steven Mnuchin. They discussed issues related to a phase one deal and agreed to maintain communication on remaining issues on phase one talks, the ministry said.

“They also discussed core issues of concern and reached a common understanding on resolving relevant problems,” it said.

Completion of a phase one deal had been expected in November. But, trade experts and people close to the White House said last week it could slide into the new year, as Beijing presses for more extensive tariff rollbacks and Washington counters with its own demands.

Washington and Beijing officials, lawmakers and trade experts say a more ambitious “phase two” trade deal looks less likely.

Tuesday's call took place amid heightened tensions on various fronts between Beijing and Washington, with China saying on Tuesday that it had summoned US Ambassador Terry Branstad on Monday to protest against the passage in the US Congress of the Hong Kong Human Rights and Democracy Act.

China's foreign ministry said the legislation amounted to interference in a Chinese internal matter.

Commerce Minister Zhong Shan, central bank governor Yi Gang and vice head of state planner Ning Jizhe also participated in the phone call.