Beijing: North Korea has staged its largest live artillery "bombardment", involving 400 long-range cannons, in the eastern town of Wonsan under the watch of leader Kim Jong-un.
The cannons, with a range of 30 kilometres, could reach Seoul if brought to the front line, South Korean media reported.
But the noisy military display, to mark the 85th anniversary of the army, stopped short of the feared nuclear weapons test or intercontinental missile launch that would have unleashed a fierce international reaction.
Tension on the Korean Peninsula was high on the anniversary, with US and South Korean missile destroyers also due to hold a live-fire exercise in the western sea on the North Korean border. The USS Michigan, a guided missile submarine, arrived in South Korea.
A meeting of the nuclear envoys of the US, South Korea and Japan in Tokyo resolved the three countries would "take strong punitive action that the North could not bear" if North Korea pushed ahead with another provocative action.
South Korea's envoy Kim Hong-kyun wouldn't give details, but said it would include stronger enforcement of United Nations Security Council resolutions, and country-level sanctions.
He said an April 28 meeting of the UN Security Council, to be chaired by US Secretary of State Rex Tillerson and attended by foreign ministers, will be pivotal in dismantling North Korea's nuclear program, Yonhap reported.
China's nuclear envoy Wu Dawei also arrived in Japan on Tuesday to exchange views on a solution on the Korean Peninsula, China's foreign ministry said.
US President Donald Trump personally lobbied UN Security Council members on Monday, telling them they must be prepared to "impose additional and stronger sanctions on North Korea".
Mr Tillerson and US Defence Secretary Jim Mattis will brief the entire US Senate on North Korea on Wednesday, unusually holding the meeting at the White House.
Chinese media have been reporting that China is likely to go beyond its ban on coal exports, and agree to cut crude oil supply to North Korea, although this hasn't been confirmed by the Chinese government.
It is believed the US and its allies are pushing for China to go further, and sanction Chinese companies and banks trading with North Korea.
The big question for Friday's UN meeting is whether China agrees to all the sanctions the US wants.
The Chinese foreign ministry has previously said any sanctions taken against North Korea must be approved through the UN Security Council, and it opposed unilateral sanctions.
The US ambassador to the UN, Nikki Haley, told American television on Monday that the Chinese pressure on North Korea was working. She said the US was "not trying to pick a fight" with Kim Jong-un: "We are not going to do anything unless he gives us a reason to do something."
"I think he's understanding that," she added.
When asked to comment on whether Chinese pressure on North Korea was working, a Chinese foreign ministry spokesman said: "China and the DPRK [North Korea] maintain normal exchanges and diplomatic channels between the two countries remain open."
On the front page of the North Korean worker's daily, the Rodong Sinmun, an editorial praised the army on its birthday and claimed "America and its puppet war maniacs" would suffer punishment with a pre-emptive strike without warning from the land and air and sea if North Korea was attacked.
DPRK Today, another government website, claimed North Korea had an "invisible" nuclear submarine missile, and the weaponry to turn US aircraft carriers, bombers and submarines into scrap iron. In the regime's usual overblown rhetoric, the website claimed mainland America would "be burnt to the ground".
South Korea's navy said it will join the approaching US aircraft carrier USS Carl Vinson for joint exercises later in the week. Japan a day earlier agreed to join the aircraft carrier for drills.
The key Chinese border port of Quanhe, which typically rumbles with several hundred trucks carrying goods between China and North Korea's Special Economic Zone, was shut on Tuesday, but expected to reopen a day later.
In Pyongyang gas prices had spiked 73 per cent and gas stations were shutting, a day after long queues for gas were observed as North Koreans stocked up in anticipation of a new round of international sanctions, Chinese media reported.
with Sanghee Liu
