Japan sent the Izumo-class helicopter carrier, the nation’s largest warship, into the South China Sea this week as part of an effort to strengthen ties with southeast Asian nations, angering the Chinese the government.

While Japan does not make any claims in the South China Sea, it has consistently opposed China’s claims the nearly the entire body of water and the islands within it. China’s claims include parts of Brunei, Taiwan, Malaysia, Vietnam, and the Philippines.

The Permanent Court of Arbitration at the Hague ruled last July that China’s claims in the region were invalid, a ruling the Chinese government vowed to ignore.

The Japanese warship sailed through the South China Sea during a week-long trip beginning Monday, with guests on board including “officers from the ten-member Association of Southeast Asian Nations (ASEAN),” according to Reuters.

The news service quotes Japanese Rear Admiral Yoshihiro Goga dismissing the idea that the ship sailed through the region “just… to show our presence,” while admitting, “from that outside that is what it looks like.” The exercise followed a meeting on military technology featuring ASEAN member nations Thailand, Vietnam, the Philippines, Indonesia, and Singapore; Reuters did not specify which ASEAN member nations joined the South China Sea warship tour.

The Izumo ship has had a busy month in the region. Last week, the Japanese warship accompanied the American USS Ronald Reagan in the South China Sea for joint military exercises, the latest in a series of such exercises in the region apparently intended to challenge China’s claims in the region.

The United States has engaged in repeated “freedom of navigation exercises” FONOPs in the South China Sea, which consist of sailing within 12 nautical miles of the territory China claims. The first such FONOP of the Trump era occurred in May, with Pentagon spokesperson, Capt. Jeff Davis repeating the military’s refrain on the region, “We fly, sail, and operate wherever international law allows,” following Chinese protests.

In March, the Chinese government vowed a “firm response” to Japan should the Izumo continue to show its face in the South China Sea, following the announcement of the tour in which the warship is currently engaged.

This week, however, the Chinese Foreign Ministry did not directly respond to the warship tour. Instead, on Thursday, spokesman Geng Shuang addressed another territorial dispute in the region: the ownership of the Senkaku, or Diaoyu, Islands in the East China Sea.

China established an Air Defense Identification Zone (ADIZ) over the Japanese islands in 2013, which would force Japanese aircraft to identify itself to China within Japanese territory. China has failed to enforce the ADIZ, as doing so could trigger American treaty duties to attack Chinese military forces.

“Diaoyu Dao and its affiliated islands have been China’s inherent territory since ancient times. China’s resolve and determination to uphold its territorial sovereignty is unwavering,” Geng told reporters Thursday. “Whatever Japan says or does, the fact that Diaoyu Dao belongs to China cannot be changed. We solemnly urge Japan to face squarely history and reality, stop provocation and educate the young generations with a correct view of history, and avoid creating new obstacles to China-Japan relations.”

China has instead reserved most of its antagonism on the South China Sea for actual claimants in the dispute. This week, Chinese officials announced that they had canceled a scheduled meeting with Vietnamese diplomats to discuss the territorial disagreement.

The meeting never happened, which Chinese officials blamed on “reasons related to working arrangements.” Vietnam claims parts of the Spratly and Paracel Islands along with the Philippines, which China has militarized by constructing artificial islands on reef territories there and equipping them with surveillance technology, surface-to-air missiles, and fighter jets.

The Chinese government propaganda outlet Global Times refuted the idea that the canceled meeting was a result of bilateral tensions.

“Foreign media outlets think the cancelation may be caused by a bilateral dispute over Vietnam’s oil and gas drilling in disputed areas of the South China Sea. No official statement has yet been made by the Vietnamese side,” a column published Thursday read. “A relaxation in the South China Sea situation is not in the desire of external powers such as the US and Japan which seek to turn the South China Sea into a place for geopolitical competition. They are more willing to see Vietnam and the Philippines make trouble for China, creating opportunities for them to interfere.”