North Korea fired a suspected ballistic missile into the sea early Tuesday, Seoul and Tokyo officials said, in the latest in a series of weapons tests by Pyongyang that raised questions about the sincerity of its recent offer for talks with South Korea.

Seoul’s Joint Chiefs of Staff said “an unidentified projectile” fired from an inland location flew toward North Korea’s eastern sea Tuesday morning. It said South Korean and U.S. intelligence authorities were analyzing details of the launch.

Japanese Prime Minister Yoshihide Suga said North Korea fired “what could be a ballistic missile” and his government stepped up vigilance and surveillance as it analyzed details of the launch.

Read:Seoul: North Korea fires 2 ballistic missiles off east coast

Tests of ballistic and cruise missiles earlier this month were North Korea’s first such launches in six months and displayed its ability to attack targets in South Korea and Japan, both key U.S. allies where a total of 80,000 American troops are stationed.

But last Friday and Saturday, Kim Yo Jong, the influential sister of North Korean leader Kim Jong Un, reached out to Seoul, saying her country was open to resuming talks and reconciliatory steps if conditions are met. Some experts said North Korea wants South Korea to work to win it relief from U.S.-led sanctions.

South Korea has called her statement “meaningful” but urged North Korea to restore communication channels before any talks between the rivals can be arranged.

The communication lines have remained largely dormant for about 15 months, so restoring them and accepting Seoul’s calls on them could be a yardstick to asses how serious the North is about its offer for conditional talks.

Read: North Korea says it tested new long-range cruise missiles

As the North conducted its third round of weapons launches on Tuesday, North Korean Ambassador Kim Song used his speech on the last day of the U.N. General Assembly to justify his country’s development of a “war deterrent” to defend against U.S. threats.

“The possible outbreak of a new war on the Korean Peninsula is contained not because of the U.S.’s mercy on the DPRK, it is because our state is growing a reliable deterrent that can control the hostile forces in an attempted military invasion,” Kim said. 

The North’s latest outreach came as a response to South Korean President Moon Jae-in’s renewed calls for a declaration to end the 1950-53 Korean War in a bid to promote peace on the Korean Peninsula. Seoul officials describe such a declaration as a “political” and “symbolic” step because a peace treaty is needed to be signed to formally end the Korean War, which ended with an armistice, leaving the peninsula in a technical state of war.

Read: In Seoul center, N Korean defectors find solace with locals

The three-year conflict pitted South Korea and U.S.-led U.N. forces against North Korea and China, killed 1 million to 2 million people. In his speech at the U.N. last week, Moon proposed the end-of-the-war declaration be signed among the two Koreas, the U.S. and China.

A U.S.-led diplomatic effort aimed at convincing North Korea to abandon its nuclear weapons in return for economic and political benefits has been stalled 2½ years. U.S. officials have repeatedly expressed hopes for further talks but have also made it clear the long-term sanctions imposed on North Korea will stay in place until the North takes concrete steps toward denuclearization.

While North Korea has tested short-range weapons and vowed to continue building its nuclear arsenal, Kim Jong Un has maintained a moratorium on testing longer-range weapons capable of reaching the American homeland, an indication he wants to keep the chances for future diplomacy with the U.S. alive.