Beijing: China hit back at US President Donald Trump on Wednesday, 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 that China had failed to rein in North Korea. The comment 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 on Twitter. “At least I know China tried!”

Trump commented the day after a 22-year-old college student died in Ohio following more than a year of imprisonment in North Korea.

A State Department spokeswoman said on Tuesday the US was considering possible steps including a ban on Americans travelling to the country.

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.

Warmbier’s death is stoking outrage in Washington and threatening to overshadow high-level US-Chinese talks on Wednesday.

Trump has been counting on China to use its economic leverage with Kim’s totalitarian government.

Top US and Chinese diplomats and defence chiefs are meeting in the US capital for security talks, and North Korea will get “top billing,” according to Susan Thornton, the senior US diplomat for East Asia.

The two world powers are trying to build on “positive momentum” created when Trump and Xi met in Florida in April, she said.

Wednesday’s discussions replace a sprawling strategic and economic dialogue held annually under the Obama administration.

It rarely produced significant results. This year’s edition separates out the security aspects, and Secretary of State State Rex Tillerson and Secretary of Defence Jim Mattis are hosting Chinese foreign policy chief Yang Jiechi and Gen. Fang Fenghui, chief of the People’s Liberation Army’s joint staff department.

Thornton said talks would cover the South China Sea, where Beijing’s island-building and construction of possible military facilities have rattled neighbours and caused tension with Washington” US-Chinese military cooperation to reduce risk of conflict” and efforts to defeat the Daesh group.

Divisive trade issues will be tackled separately at a later date.