The five-day Vigilant Ace drill – involving 230 aircraft, including F-22 Raptor stealth jet fighters, and tens of thousands of troops – began Monday morning, Seoul’s air force said, AFP reported.

Pyongyang over the weekend blasted the drill, accusing US President Donald’s Trump’s administration of “begging for nuclear war”.

The annual exercise comes five days after the nuclear-armed North test-fired a new ICBM, which it says brings the whole of the United States within range.

As tensions surged, US Senator Lindsey Graham, an influential Republican and foreign policy hawk, warned that the US was moving closer to “preemptive war” with the North.

“If there’s an underground nuclear test (by the North), then you need to get ready for a very serious response by the United States,” Graham told the CBS show Face the Nation.

The isolated and impoverished North has staged six increasingly powerful atomic tests since 2006 – most recently in September.

“The preemption is becoming more likely as their technology matures. Every missile test, every underground test of a nuclear weapon, means the marriage is more likely,” he said.

Graham’s remarks echoed those of Trump’s National Security Adviser HR McMaster, who told a security forum on Saturday that the potential for war with the North “is increasing every day”.

The North has boasted that the Hwasong 15 ICBM tested on Wednesday is capable of delivering a “super-large” nuclear warhead anywhere in the US mainland.

Analysts agree that the latest test showed a big improvement in potential range, but say it was likely achieved using a dummy warhead that would have been quite light.

They say a missile carrying a much heavier nuclear warhead would struggle to travel as far.

They are also skeptical that Pyongyang has mastered the sophisticated technology required to protect such a warhead from the extreme temperatures and stresses encountered as the missile hurtles back to Earth.

The North’s widely-condemned nuclear and missile programmes have made significant progress under leader Kim Jong-Un, who has overseen four nuclear tests and dozens of missile launches since taking power in 2011.

The months-long nuclear standoff between Kim and Trump – as well as their trading of personal insults – has fuelled concerns of another conflict, more than six decades after 1950-53 Korean War that left much of the peninsula in ruins.

But even some Trump advisers say US military options are limited when Pyongyang could launch an artillery barrage on the South Korean capital Seoul – only around 50km from the heavily-fortified border and home to 10 million people.

Outdoor air pollution has long been linked to major health conditions such as heart disease, stroke, cancer, asthma and chronic obstructive pulmonary disease. A new study now adds kidney disease to the list, according to researchers at Washington University School of Medicine in St. Louis and the Veterans Affairs (VA) St. Louis Health Care System.

The Washington University team, in collaboration with scientists at the Veterans Affairs’ Clinical Epidemiology Center, culled national VA databases to evaluate the effects of air pollution and kidney disease on nearly 2.5 million people over a period of 8.5 years, beginning in 2004. The scientists compared VA data on kidney function to air-quality levels collected by the Environmental Protection Agency (EPA) as well as the National Aeronautics and Space Administration (NASA).

The EPA derived its data from land-based air-monitoring stations across the U.S. The findings suggest that 44,793 new cases of kidney disease and 2,438 new cases of kidney failure may be attributed to levels of air pollution that exceed the EPA’s threshold of 12 micrograms per cubic meter of air, which is the highest level of air pollution considered safe for the public, as set by the Clean Air Act of 1990 and updated in 2012.

The study is published Sept. 21 in the Journal of the American Society of Nephrology.

“Data on the relationship between air pollution and kidney disease in humans has been scarce,” said Ziyad Al-Aly, MD, the study’s senior author and an assistant professor of medicine at Washington University. “However, once we analyzed the data, the link between air pollution and the development of kidney disease was clear.”

Fine particles can damage the kidneys in the same way they damage other organs such as the heart and lungs. Airborne and invisible, microscopic pieces of dust, dirt, smoke, soot and liquid droplets often become destructive when they invade the bloodstream. The kidneys filter the blood, and these harmful particles can disrupt normal kidney function.

The study found that even low levels of particulate matter may adversely affect the kidneys. And those adverse effects increase as pollution levels increase.

“The higher the levels of air pollution, the worse it is for the kidneys,” said Al-Aly, who is also the VA’s director of clinical epidemiology in St. Louis. “However, no level is completely safe. Even at relatively low levels, there was a relationship between particulate matter concentrations below the EPA thresholds and kidney disease.”

Researchers also linked the VA data to space-borne sensors from NASA satellites. “NASA data and EPA data yielded consistent results,” Al-Aly said.

“The beauty of using both EPA and NASA data is that the agencies used two distinct techniques for collecting data, yet the results were similar,” he said. “This constellation of findings suggests that chronic exposure to air pollution is a significant risk factor for the development and progression of kidney disease.”

Study results placed Southern California and large regions in the South, Midwest and Northeast at the greatest risk for kidney decline attributed to air pollution.

Over the years, unsafe levels of outdoor air pollution have decreased in the U.S. Still, more than half of the U.S. population lives in areas — from industrialized big cities to farming communities to coal-mining towns — with unhealthy levels of outdoor air pollution, according to a 2016 study by the American Lung Association.

In many places across the globe, including China and India, outdoor air pollution is significantly worse than in the U.S.

“In our analyses, the risk of chronic kidney disease and its progression was most pronounced at the highest levels of fine particulate matter concentration,” Al-Aly said. “This suggests further study is needed for a broader assessment of the global burden of kidney disease attributable to air pollution.”

The Iranian Air Defense is at the forefront of protection of Iran’s dignity and existence, Ayatollah Khamenei said in a meeting with the Air Defense commanders and officials in Tehran on Sunday.

The Leader also admired the “very good jobs” that the Khatam al-Anbia Air Defense Base has done, describing them as a testimony to the “determination, motivation and capabilities” of local forces.

The key to removing the obstacles is the existence of “educated, prudent, courageous and tireless human resources” in the country, Imam Khamenei added, calling on the Air Defense to accelerate efforts and develop “new and innovative plans” to make Iran self-sufficient.