North Korea says it successfully test-fired newly developed long-range cruise missiles over the weekend, its first known testing activity in months, underscoring how it continues to expand its military capabilities amid a stalemate in nuclear negotiations with the United States.

The Korean Central News Agency said Monday the cruise missiles, which had been under development for two years, demonstrated an ability to hit targets 1,500 kilometers (932 miles) away during flight tests on Saturday and Sunday.

The North hailed its new missiles as a “strategic weapon of great significance” that meets leader Kim Jong Un’s call to strengthen the country’s military might, implying that they were being developed with an intent to arm them with nuclear warheads.

North Korean state media published photos of a projectile being fired from a launcher truck and an apparent missile with wings and tail fins traveling in the air.

South Korea’s Joint Chiefs of Staff said the military was analyzing the North Korean launches based on U.S. and South Korean intelligence. The U.S. Indo-Pacific Command said it was monitoring the situation with allies and that the North Korean activity reflects a continuing focus on “developing its military program and the threats that poses to its neighbors and the international community.” Japan said it was “extremely concerned.”

Kim during a congress of the ruling Workers’ Party in January doubled down on his pledge to bolster his nuclear deterrent in the face of U.S. sanctions and pressure and issued a long wish list of new sophisticated assets, including longer-range intercontinental ballistic missiles, nuclear-powered submarines, spy satellites and tactical nuclear weapons. Kim also said then that his national defense scientists were developing “intermediate-range cruise missiles with the most powerful warheads in the world.”

North Korea’s weapons tests are meant to build a nuclear and missile program that can stand up to what it claims as U.S. and South Korean hostility, but they are also considered by outside analysts as ways to make its political demands clear to leaders in Washington and Seoul.

The North’s resumption of testing activity is likely an attempt at pressuring the Biden administration over the diplomatic freeze after Kim failed to leverage his arsenal for economic benefits during the presidency of Donald Trump.