BEIJING (Reuters) – China on Thursday pledged a firm response if Japan stirs up trouble in the South China Sea, after Reuters reported on a Japanese plan to send its largest warship to the disputed waters.

The Izumo helicopter carrier, commissioned only two years ago, will make stops in Singapore, Indonesia, the Philippines and Sri Lanka before joining the Malabar joint naval exercise with Indian and U.S. naval vessels in the Indian Ocean in July, sources told Reuters.

The trip would be Japan’s biggest show of naval force in the region since World War Two.

“If Japan persists in taking wrong actions, and even considers military interventions that threaten China’s sovereignty and security… then China will inevitably take firm responsive measures,” Foreign Ministry spokeswoman Hua Chunying said at a regular press briefing.

China said on Tuesday that it was waiting for an official word on why Japan plans to send the warship on the tour through the South China Sea, but that it hoped Japan would be responsible.

Hua did not say on Thursday if China had received confirmation of the plan, but said that the South China Sea issue did not involved Japan and that the country should “reflect deeply” on its “disgraceful” past invasion of the Paracel and Spratly Islands.

Japan controlled the islands during World War Two until its surrender in 1945.

China claims almost all the South China Sea and its growing military presence in the waterway has fueled concern in Japan and the West, with the United States holding regular air and naval patrols to ensure freedom of navigation.

Taiwan, Malaysia, Vietnam, the Philippines and Brunei also claim parts of the sea which has rich fishing grounds, oil and gas deposits and through which around $5 trillion of global sea-borne trade passes each year.

Japan does not have any claim to the waters, but has a separate maritime dispute with China in the East China Sea.

China regularly states that the dispute should be resolved without interference from non-claimants.

Beijing has been speaking with 10 members of the Association of South East Asian Nations since 2010 to agree to a set of rules aimed at avoiding conflict in the South China Sea.

Addressing a news conference at the end of the annual meeting of China’s parliament on Wednesday, Chinese Premier Li Keqiang said that China hopes to push forward with the negotiations for the code of conduct to maintain stability.

(Reporting by Beijing Newsroom; Writing by Christian Shepherd; Editing by Nick Macfie)