BEIJING (Bloomberg) - China hit back at US President Donald Trump on Wednesday (June 21), saying its efforts on North Korea have been "indispensable".

China has "played an important and constructive role" in seeking peace on the Korean peninsula, Foreign Ministry spokesman Geng Shuang told reporters in Beijing.

China strictly implements United Nations Security Council resolutions and isn't the crux of the North Korean issue, he said.

The remarks came a day after Trump said on Twitter that China had failed to rein in North Korea.

The comment, which came after a 22-year-old college student died in Ohio following more than a year of imprisonment in North Korea, suggested he's weighing new options to deal with a regime that's vowed to develop nuclear weapons capable of striking the US mainland.

"While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out," Trump wrote. "At least I know China tried!"

The spat underscores the risk of conflict between the world's biggest economies even as the overall relationship is on more stable ground than when Trump took office in January.

Top diplomats and defence chiefs from the two nations will meet in Washington later on Wednesday, while China separately has invited Trump's daughter Ivanka and son-in-law Jared Kushner to visit Beijing later this year.

China provides most of North Korea's food and fuel imports. It has backed the Kim dynasty since the Korean War, in part to keep US troops away from its border.

While China has taken some steps on North Korea - including halting coal purchases this year after Kim's estranged half-brother was murdered in Malaysia - its efforts haven't produced a breakthrough so far.

One focus of Wednesday's meeting in Washington will be to target North Korean companies that do business via China, Acting Assistant Secretary of State Susan Thornton told reporters on June 19.

Otto Warmbier, who was held for allegedly stealing a propaganda banner, was returned to the US last week in a coma.

Trump said afterward the US should have secured his release sooner, calling his treatment "a disgrace" and the North Korean government "a brutal regime".

The furore in the US over Warmbier's death recalls the raw emotions felt after a chemical weapons attack in Syria killed children, prompting Trump to fire cruise missiles at an airbase operated by President Bashar al-Assad's regime.

Yet dropping bombs on Kim Jong Un's nation - an option the US says remains on the table - is so risky that many analysts see it as implausible because of North Korea's ability to launch a devastating attack on its neighbours in North Asia.

Warmbier's death is "an outrage even by North Korean standards," said John Delury, an associate professor of Chinese studies at Yonsei University in Seoul. "It does demand something that's beyond the typical response. But what do you do? How do you punish North Korea? The instinctive response, such as a travel ban, would not punish the people who killed Otto Warmbier."

Spy satellites have detected what appear to be modifications around a tunnel entrance to an underground test area at North Korea's nuclear test site, CNN reported on Wednesday, citing two US officials it did not identify. It said military options for North Korea had been updated and would be presented to Trump.

Trump's administration talked up the threat of military action earlier this year, sending aircraft carrier strike groups to the region. In April, Chinese Foreign Minister Wang Yi warned a war would devastate the region.

Since then, things had appeared to calm down. North Korea has refrained from testing a nuclear device and is yet to test an intercontinental ballistic missile capable of carrying a nuclear warhead.

In turn, US officials focused on diplomatic efforts. The new government in South Korea has repeatedly said it wants to use both sanctions and dialogue to rein Kim in.

In one interview, Trump appeared to empathise with Kim, telling Reuters that taking over North Korea after his father's death was "a very hard thing to do".

He told Bloomberg in May he'd be open to meeting Kim under the right conditions.

The Wall Street Journal reported on Sunday (June 18) that US diplomats have held discussions for more than a year with North Korea's top nuclear negotiator, focused on freeing American prisoners. Warmbier's death undercuts any progress from those meetings.

"This makes dealing with Kim Jong Un so toxic," Ralph Cossa, president of the Pacific Forum CSIS in Honolulu. "If there are any US preconditions for the talks, the number one priority has to be the release of the three other prisoners."