IN a defiant bit of timing, South Korea announced that key parts of a contentious US missile defense system had been installed a day after rival North Korea showed off its military power.

The South’s trumpeting of progress on setting up the Terminal High-Altitude Area Defense system, or THAAD, comes as high-powered US military assets converge on the Korean Peninsula and as a combative North Korea signals possible nuclear and missile testing.

North Korea conducted live-fire artillery drills on Tuesday, the 85th anniversary of the founding of its million-person strong Korean People’s Army.

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On the same day, a US guided-missile submarine docked in South Korea.

And the aircraft carrier USS Carl Vinson is also headed toward the peninsula for a joint exercise with South Korea.

The moves to set up THAAD within this year have angered not only North Korea, but also China, the country that the Trump administration hopes to work with to rid the North of nuclear weapons.

China, which has grown increasingly frustrated with its ally Pyongyang, and Russia see the system’s powerful radars as a security threat.

South Korea said in a statement Wednesday that unspecified parts of THAAD were installed.

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The statement said that Seoul and Washington have been pushing to get THAAD quickly working to cope with North Korea’s advancing nuclear and missile threats.

According to Yonhap news agency, the parts include two or three launchers, intercept missiles and a radar.

About 8,000 police officers were mobilized, and the main road leading up to the site in the country’s southeast was blocked earlier Wednesday, Yonhap reported.

About 200 residents and protesters rallied against THAAD in front of a local community centre, some hurling plastic water bottles.

On Tuesday, North Korea conducted what it called its largest ever combined live-fire drills, near the east coast port city of Wonsan.

North Korea’s official media reported Wednesday that leader Kim Jong-un personally observed the exercises, which involved the firing of more than 300 large-caliber artillery pieces and included submarine torpedo-attacks on mock enemy warships.

Along with sending U.S. military assets to the region in a show of force, President Donald Trump is leaning on China to exert economic pressure on its wayward ally.

Chinese President Xi Jinping, who spoke to Trump on Monday, is urging restraint from both Pyongyang and Washington.

In Washington, top Trump administration officials are due to brief the entire U.S. Senate on Wednesday.

A rapid tempo of North Korean weapons testing in the past year has pushed Kim Jong-un’s authoritarian nation closer to developing a nuclear-tipped missile that could reach the U.S. mainland.

Republican Sen. Lindsey Graham voiced confidence that Trump won’t allow North Korea to reach that point.

Graham, a defence hawk who dined with Trump on Monday night, said the North should not underestimate the president’s resolve.

The USS Michigan, a nuclear-powered submarine, arrived Tuesday at the South Korean port of Busan for what was described as a routine visit to rest crew and load supplies.

The U.S. 7th Fleet said two American destroyers were conducting simultaneous maritime exercises with naval ships from South Korea and Japan.

North Korea routinely accuses the United States of readying for an invasion, and threatens pre-emptive strikes to stop it.

An unnamed North Korean Foreign Ministry spokesman said the U.S. administration’s policy to maximize pressure on North Korea was “little short of lighting the fuse of total war,” the state news agency reported Tuesday.

The streets of Pyongyang, however, were quiet for Tuesday’s anniversary, which was overshadowed by April 15 celebrations for the birthday of the nation’s late founder Kim Il-sung, and were marked by a missile test the following day.

The Trump administration is also upping the ante diplomatically. On Friday, Secretary of State Rex Tillerson will chair a special meeting of the U.N. Security Council.

Tillerson will be “very vocal” about nations enforcing sanctions on North Korea, State Department spokesman Mark Toner said.

Trump said Monday the council must be prepared to impose stronger sanctions.

NORTH KOREAN ECONOMY HIT HARD

CHINA’S push to use its trading clout to hurt North Korea is starting to be felt as new figures show a sharp drop in imports.

New figures show that Chinese imports from North Korea fell 35 per cent month-on-month in March, after Beijing suspended coal purchases to punish its nuclear-armed neighbour for missile tests.

Total imports from the North by China — Pyongyang’s sole major diplomatic ally and chief trading partner — stood at US$114.56 million (AU$151 million) last month, down from US$176.7 million (AU$233 million) in February, according to Chinese customs data.

Beijing on February 18 imposed a total halt on coal imports from the North until the end of 2017, hardening its stance after a new missile test by Pyongyang, in line with new sanctions adopted by the UN Security Council.

The halt in coal exports aims to cut off a crucial supply of hard currency for Kim Jong-un’s regime.

In 2016 China imported coal worth some US$1.19 billion (AU$1.57 billion) from the North.

But Beijing has maintained exports to the Stalinist regime.

North Korea last month bought from its powerful neighbour some US$29.1 million (AU$38.5 million) of electrical appliances and components, US$21.5 million (AU$28.4 million) of plastics and manufactured components, and US$23.9 million (AU$31.6 million) of synthetic fibres — most of which go back across the border in the form of finished clothes.

US President Donald Trump has been pushing Chinese President Xi Jinping to use his economic clout over Pyongyang to bring the rogue regime to heel.

However, Beijing is concerned that a regime collapse could trigger a flood of refugees across the border and leave the US military on its doorstep.

“The last thing China wants is to see war break out in the region ... given the geopolitical circumstances, (North Korea) must learn to be as flexible as they are determined,” the state-run Global Times newspaper said overnight.

Meanwhile, Mr Trump told members of the United Nations Security Council at the White House that the “status quo” on North Korea is “unacceptable”.

“The council must be prepared to impose additional and stronger sanctions,” Mr Trump said.

He reportedly told journalists that “I’m not so sure he’s so strong like he says he is.”

It came as North Korea held major live-fire drills to mark the 85th founding anniversary of its military.

(LEAD) N. Korea stages firing drill marking military anniv.: source https://t.co/Ku6331vjOB — Yonhap News Agency (@YonhapNews) April 25, 2017

South Korea’s Yonhap news agency cited a government source as saying the exercise was the North’s ‘largest ever’.

“Signs are detected that North Korea’s military is conducting a large-scale drill around the eastern port city of Wonsan on the anniversary,” a source told Yonhap News.

North Korea will cross the point of no return if it carries out another nuclear test, the official Chinese newspaper Global Times, controlled by the ruling Communist Party, warns.