SEOUL, South Korea (AP) — The South Korean and US militaries launched their biggest joint military exercises in years Monday, as North Korea said it conducted submarine-launched cruise missile tests in apparent protest of the drills it views as an invasion rehearsal.

North Korea’s missile tests Sunday signal the country likely will conduct provocative weapons testing activities during the US-South Korean drills that are to run for 11 days. Last week, North Korean leader Kim Jong Un ordered his troops to be ready to repel its rivals’ “frantic war preparation moves.”

The South Korean-US drills include a computer simulation called the Freedom Shield 23 and several combined field training exercises, collectively known as the Warrior Shield FTX.

South Korean and US authorities didn’t immediately disclose details of Monday’s drills.

But they said earlier the computer simulation is designed to strengthen the allies’ defence and response capabilities amid North Korea’s increasing nuclear threats and other changing security environments. They said the field exercises would also return to the scale of their earlier largest field training called Foal Eagle that was last held in 2018.

A recent US military statement said the field exercises are to further enhance the two militaries’ “cooperation through air, land, sea, space, cyber and special operations, and improve upon tactics, techniques and procedures.”

North Korea said in state media that its launches of two cruise missiles from a submarine off its east coast showed its resolve to respond with “overwhelming powerful” force to the intensifying military maneuvers by the “the US imperialists and the South Korean puppet forces.”

The North’s official Korean Central News Agency on Monday called the missiles “strategic” weapons and said their launches verified the operation posture of the country’s “nuclear war deterrence.” This implies that North Korea aims to arm the cruise missiles with nuclear warheads.

It said the missiles flew for more than two hours, drawing figure-eight-shaped patterns and hit targets 1,500 kilometres (930 miles) away. The missiles were fired from the 8.24 Yongung ship, KCNA said, referencing a submarine that North Korea used to conduct its first submarine-launched ballistic missile test in 2016.

The reported launch details show Japan, including US military bases in Okinawa, is within striking distance of the cruise missiles, if they are fired from the North’s eastern waters, said Kim Dong-yub, a professor at the University of North Korean Studies in Seoul. He added the weapons could reach even the US Pacific territory of Guam if the submarine could operate at a greater distance from North Korean waters.

Sunday’s actions were the North’s first underwater missile launches since it test-fired a weapon from a silo under an inland reservoir last October. Last May, the country test-launched a short-range ballistic missile from the same submarine.