Meanwhile, Japan's Kyodo News agency reported that the Japanese government had refused to accept Beijing's conditions for a meeting between the countries' leaders not long after tensions over the islands worsened last year.

Beijing had proposed that both sides temporarily put aside their claims to the islands and keep all government ships outside the 12-mile zone as prerequisites for a meeting between the countries' top leaders, the report said.

However, Tokyo rejected the proposal, as it would require it to acknowledge formally that the islands' sovereignty was in dispute.

Japan contends they have been its legal possessions since the late 19th century.

On Wednesday, Japanese Prime Minister Shinzo Abe said in London that he wanted to have dialogue with President Xi Jinping .

Xi and Abe have still not even talked on the phone, despite visits to Beijing by several senior Japanese officials to pave the way for a meeting.

"The Chinese government's bottom line had been very strong and consistent," said Shi Yongming , a research fellow with the China Institute of International Studies. "The Japanese must accept that the islands are under dispute.

"If they can accept that, the dispute can be put aside for more constructive negotiations to improve the overall relations between the two countries.

"If they continue insisting that there is no dispute at all, the top leaders of these two nations will never meet."

Beijing argues that the islands should have been returned to China when Japan surrendered the rest of its imperial possessions after the end of the second world war.