The US and South Korea began their largest-ever live-fire drills near the border with North Korea, which has threatened retaliation against the two nations it labels “war maniacs.”

The first day of drills took place less than 40 kilometers (25 miles) from the border Thursday and are expected to run through June 15. Some 2,500 soldiers and 610 pieces of equipment, including fighter jets and rocket launchers, participated in the exercises that began around 2:30 pm local time, according to a spokesperson at South Korea’s Ministry of National Defense.

The event is meant to better prepare the two allies to work together against North Korea as it ramps up its provocations, South Korea’s military earlier said.

The drills add to the display of force by South Korea and the US as they mark the 70th anniversary of an alliance forged during the Korean War. Additional cooperation is expected to come after South Korean President Yoon Suk Yeol and President Joe Biden agreed last month on a plan for the US to keep deploying nuclear assets —including submarines — in the region, and for Seoul to have a greater say in how America utilizes its nuclear umbrella.

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Yoon, who took office a year ago, has worked to restore joint drills with the US that had been suspended or scaled back under his predecessor, Moon Jae-in, and former President Donald Trump, as they sought a rapprochement with Pyongyang. Those efforts resulted in three face-to-face meetings between Trump and Kim Jong Un but no concrete steps to reduce North Korea’s atomic arsenal — which only grew larger as talks fizzled.

After starting the year firing off rockets at a blistering pace, Kim’s regime has not launched a ballistic missile for more than a month. But the last one marked a major development for the country’s program, with the test-launch of its first solid-fuel intercontinental ballistic missile, designed to deliver a nuclear warhead to the US mainland.

The country’s current ICBM inventory is comprised of liquid-fuel rockets, which take more time to prepare and fill with propellant, opening a window of vulnerability for them to be shot on the pad before taking off. North Korea has rolled out a variety of new solid-fuel ballistic missiles over the past few years designed to strike South Korea and Japan, which together host the bulk of America’s military personnel in the region.

--With assistance from Seyoon Kim.

(Updates with details of first day.)