SEOUL, South Korea (AP) — North Korea launched another ballistic missile toward its eastern waters Thursday, officials said, conducting its third round of weapons testing this week as South Korean and US troops continue joint military exercises that Pyongyang considers a threat.

The latest launch also came hours before South President Yoon Suk Yeol was to travel to Tokyo for a summit with Japanese Prime Minister Fumio Kishida aimed at mending frayed ties and solidifying a trilateral security cooperation with the United States to counter North Korean threats.

South Korea's Joint Chiefs of Staff said the launch occurred Thursday morning but did not immediately give further details, such as how far the missile flew.

The Japanese Defense Ministry said the missile was fired from a western coastal area of North Korea and was expected to go down at sea about an hour later, around 550 kilometres (340 miles) off the North's east coast and outside the Japanese Exclusive Economic Zone.

Pyongyang had already staged two launch events this week, firing cruise missiles from a submarine and also sending short-range ballistic missiles across its territory and toward an eastern sea target.

The weapons tests have been widely expected as North Korean leader Kim Jong Un last week ordered his military to be ready to repel what he called "frantic war preparations moves" by his country's rivals.

The US-South Korean drills, which the North views as a rehearsal for invasion, began Monday and are scheduled to continue until March 23. They include computer simulations and live-fire field exercises.

Last year Pyongyang test-fired more than 70 missiles, including nuclear-capable ones that could reach South Korea, Japan and the US mainland. North Korea said many of those tests were a warning over previous South Korean-US military drills.

The South Korea-Japan summit was arranged after Yoon's government last week took a major step toward repairing bilateral ties strained by Japan's 1910-45 colonial rule of the Korean Peninsula.

Yoon's government said it would use local funds to compensate Koreans forced into industrial slave labour during the colonial rule without contributions from Japanese companies that employed them.

The plan, which met fierce domestic opposition, reflected the Yoon government's resolve to improve ties with Japan and boost a Seoul-Tokyo-Washington security cooperation.

Under Kishida, Tokyo has also made a major break from its post-World War II principle of self-defense only, adopting a new national security strategy in December that includes the goals of acquiring pre-emptive strike capabilities and cruise missiles to counter growing threats from North Korea, China and Russia.