Led by a 10,000 ton-class large destroyer, a group of warships of the Chinese People’s Liberation Army (PLA) Navy reportedly sailed beyond the first island chain on Wednesday via two strategically important straits near Japan, a routine exercise experts said on Thursday sent a signal amid Japan’s recent militaristic moves, including updates to its national security strategies with the plan to increase military spending and referring to China as a “strategic challenge.”

Japan’s Maritime Self-Defense Force spotted a PLA Navy flotilla consisting of the Type 055 large destroyer Lhasa, the Type 052D destroyer Kaifeng and the Type 903A replenishment ship Taihu sailing from the East China Sea through the Osumi Strait into the West Pacific from Tuesday to Wednesday and a PLA Navy electronic reconnaissance vessel with hull number 796 sailing from the East China Sea through the Miyako Strait into the West Pacific from Monday to Wednesday, Japan’s Ministry of Defense Joint Staff said in two press releases on Wednesday.

This is the second time the Lhasa has made a voyage into distant waters this year, with the first one in June, when it led a flotilla of a similar configuration into the Sea of Japan, and then sailed in a circle around Japan before returning, according to releases by Japan’s Ministry of Defense Joint Staff at the time.

The latest voyage is likely a regular far sea training exercise carried out according to training schedules, which is aimed at enhancing the Lhasa and other vessels’ operational capabilities in far sea, a Beijing-based military expert told the Global Times on Thursday, requesting anonymity.

It also comes at a time when Japan recently updated its national security strategies, which plan to increase the country’s military spending and referred to China as a “strategic challenge.”

Japan is also planning to purchase Tomahawk cruise missiles from the US, which experts believe are of a type of aggressive, standoff weapon that can be used in first attacks, going against Japan’s pacifist constitution set after Japan’s defeat in World War II.

It also came after a senior official of Japan’s ruling Liberal Democratic Party recently also visited the island of Taiwan and made irresponsible remarks on China.

While the PLA warships’ far sea training is routine and not aimed at any third party, it will display the PLA’s capabilities in safeguarding China’s national sovereignty, territorial integrity and development interests, as well as defending the post-World War II international order, the expert said.