Tokyo: Prime Minister Yoshihide Suga had voiced "grave concerns" over China's aggressive actions in surrounding waters in phone talks with Indian counterpart Narendra Modi.

According to Kyodo News, Suga on Monday relayed Tokyo's worries about Beijing's "intensifying unilateral attempts to change the status quo" in the East and South China seas, including the recent introduction of a law allowing its coast guard to use weapons against ships it views as intruding into its territory, according to the Foreign Ministry.

The leaders affirmed the importance of Japan and India cooperating to realize a "free and open Indo-Pacific" region, the ministry said, along with other countries including the United States and Australia.

The four countries, also known as the Quad, have been bolstering ties as a counter to China's growing economic and military clout, as reported by Kyodo News.

Beijing is embroiled in a number of territorial disputes, including in the East China Sea over the Japanese-administered Senkaku Islands, which it claims and calls Diaoyu. It has also continued the militarization of artificial islands in the disputed South China Sea despite an international ruling in 2016 against its claims.

The European Union also has slammed China's activities in the South China Sea, accusing it of threatening regional peace and stability.

On Saturday, the bloc issued a statement saying it strongly opposed "unilateral actions that could undermine regional stability and the international rules-based order".

China claims sovereignty over almost the entire South China Sea and has overlapping territorial claims with Brunei, Malaysia, the Philippines, Vietnam and Taiwan.

China has been increasing its maritime activities in both the South China Sea and the East China Sea over the past few months, partly in response to Beijing's concerns over the increasing US military presence in the region because of escalating Sino-US tensions.

Beijing's rising assertiveness against counter claimants in the East and South Sea has resulted in unprecedented agreement across the Indo-Pacific.