A senior US diplomat said on Tuesday he hopes China will accept an offer for a technical briefing on a new missile defence system the United States wants to deploy in South Korea, a prospect Beijing sees as a threat to its national security.
US Deputy Secretary of State Anthony Blinken said the Terminal High Altitude Area Defence (THAAD) system was necessary for the United States to protect itself and regional allies from North Korean missile attacks.
"We realize China may not believe us and also proposed to go through the technology and specifications with them ... and prepared to explain to what the technology does and what it doesn't do and hopefully they will take us up on that proposal," Blinken told Washington's Brookings Institution.
Blinken spoke ahead of a visit by Chinese President Xi Jinping to Washington for a nuclear security summit that will have concerns about North Korea high on the agenda.
The United States and South Korea agreed to begin talks on possible THAAD deployment last month after North Korea tested its fourth nuclear bomb on Jan 6 and launched a long-range rocket on Feb 7.
China backed tough new sanctions on North Korea following the tests but has voiced opposition to THAAD as its radar has a range that would extend far beyond the Korean peninsula and into China.
South Korea's military said on Tuesday that North Korea test fired a short-range missile on its east coast in the latest of a string of launches that Pyongyang has characterised as a response to the sanctions.
US President Barack Obama will meet South Korean President Park Geun hye and Japanese Prime Minister Shinzo Abe on Thursday to discuss North Korea's nuclear program, ahead of a bilateral meeting between Obama and Xi later that day.
Blinken said THAAD deployment was a necessary step until Pyongyang's behaviour changed.
"None of these steps are directed against China but we have also been very clear that as long as this persists ... we will have to take steps," he said.
Obama's deputy national security adviser, Ben Rhodes, said China had stepped up pressure on North Korea, but this had to be shown to change Pyongyang's calculus.
"We've had good support from China, but we clearly believe that there's more that will continue to have to be done, including on enforcing the sanctions we have put into place," Rhodes told reporters.