Chinese President Xi Jinping urged "restraint" over North Korea in a phone call with Donald Trump Monday, as Japan joined exercises with an American supercarrier heading to the Korean peninsula.
The US leader has repeatedly called on China, the North's sole major ally, to do more to rein in Pyongyang, as tensions in the region soar amid speculation it will conduct another nuclear test.
"(China) hopes that the relevant parties can maintain restraint and avoid actions that would increase tensions in the Korean peninsula," Xi said, according to the foreign ministry.
"The only way to realise denuclearisation in the Korean peninsula and quickly resolve North Korea's nuclear problem is for each relevant party to fulfil its duties."
The conversation -- the second since their summit at Trump's luxury resort in Florida early this month -- highlights rising concern in Beijing that tensions between Washington and Pyongyang could spiral into military conflict.
"The international situation is rapidly changing, it is essential that China and the US maintain a close contact and exchange opinions on important matters in a timely manner," Xi told Trump.
Trump also spoke to Japanese Prime Minister Shinzo Abe on Monday, discussing the joint drills under way between the US carrier Carl Vinson and Japan's Maritime Self-Defence Force.
"We completely agreed that we strongly demand restraint by North Korea, which has repeatedly taken dangerous provocative actions," Abe told reporters after the call.
Tensions have soared in recent months as North Korean missile tests have brought ever-more bellicose warnings from Trump's administration -- and repeated demands for China do more to help.
Despite its longstanding ties with the North, China has stepped up pressure, announcing in February that it was halting all imports of coal from North Korea -- a crucial earner for Pyongyang -- for the rest of the year.
It also issued a stern warning earlier this month that a conflict over North Korea could break out "at any moment".
The comments came ahead of a failed missile test a day after the 105th anniversary of the birth of North Korea's founder Kim Il-Sung.
Missile and nuclear tests are often timed around major dates and speculation is now focused on Tuesday's anniversary of the founding of its military.
- 'China can do more' -
US Vice President Mike Pence said Saturday that the Vinson and its strike group would arrive in the Sea of Japan (East Sea) -- which sits between the Korean peninsula and Japan -- "in a matter of days".
South Korea also said it was considering drills with the carrier group, which is currently conducting joint exercises with Japan in the Philippine Sea.
Confusion had clouded the carrier's whereabouts after Trump earlier indicated the "armada" was steaming towards North Korea when in fact it was heading south and was photographed off Java.
The North's ruling party newspaper on Monday called the Vinson's deployment "undisguised military blackmail".
"Such threat may startle a jellyfish, but can never work on the DPRK," it said, using the country's official name.
A separate editorial on the North's propaganda website Uriminzokkiri said the dispatch of the Carl Vinson signalled "that an invasion of the North is nearing day by day".
In the event of an attack, it said, "The world will witness how Washington's rash nuclear aircraft carriers are turned into a huge pile of steel and buried at sea and how a country called America is wiped out from the Earth."
Pyongyang has also detained a US citizen -- Kim Sang-Duk, or Tony Kim, who was lecturing at a foreign-funded university in Pyongyang, the university said Monday.
Two other US citizens -- college student Otto Warmbier and Korean-American pastor Kim Dong-Chul -- are currently being held in the North after sentenced to long prison terms.
North Korea has arrested and jailed several US citizens in the past decade, often releasing them only after high-profile visits by current or former US officials or former US presidents.
The new US president has indicated he will not allow North Korea to achieve its goal of developing an intercontinental ballistic missile capable of delivering a nuclear warhead to the western United States.
Pyongyang insists it needs a powerful arsenal -- including atomic weapons -- to protect itself from what it says is the ever-present threat of invasion by hostile US forces.