Japan has warned China that ties are “deteriorating markedly” over disputed East China Sea islets, as China’s envoy in Tokyo reiterated Beijing’s stance that the specks of land were its territory and called for talks to resolve the row.

Tensions between Asia’s two largest economies have risen since Japan saw an increasing number of Chinese coastguard and other government ships sailing near the disputed islets – called Senkaku in Japan and Diaoyu in China – over the past few days.

Fumio Kishida, Japan’s foreign minister, called in the Chinese ambassador, Cheng Yonghua, for the second time since Friday and told him that China was trying to change the status quo unilaterally, a Japanese foreign ministry statement said. It also said Kishida told Cheng that the environment surrounding Sino-Japanese ties was deteriorating markedly.

A file photo from 2011 shows a Japanese surveillance plane flying by the islands. Photograph: AP

Cheng said after the meeting that he told Kishida the islands were an integral part of China’s territory and that the dispute should be resolved through diplomacy and dialogue.

“I told him that … it is natural that Chinese ships conduct activity in the waters in question,” he told reporters. “I also told him both countries need to work on dialogue through diplomatic channels so as not to make things more complicated and escalated.”

Dozens of Chinese vessels were spotted near the islands at the weekend. The flurry of Chinese incursions into the waters follows a period of sustained pressure on China about its activities in the South China Sea. The US, its south-east Asian allies and Japan have questioned Chinese land reclamation on contested islands in the South China Sea, particularly since an international court rejected China’s historic claims to most of that sea last month.

China has refused to recognise the court ruling on a case brought by the Philippines. Japan called on China to adhere to it, saying it was binding but Beijing warned Japan not to interfere.

Ties between China and Japan, the world’s second and third largest economies, have been plagued by the territorial row, the legacy of Japan’s wartime occupation of parts of China and regional rivalry.