The report comes after the Japanese government apparently reached a deal with private landowners to buy part of a chain of islands in the East China Sea that it calls Senkaku, but which Beijing claims under the name Diaoyu.

Prime Minister Yoshihiko Noda will probably not meet Chinese President Hu Jintao over the weekend in Russia, Kyodo News agency reported, citing unnamed government sources.

The two will be among leaders gathering in Vladivostok for the Asia-Pacific Economic Cooperation (APEC) summit on Saturday and Sunday.

Instead of a formal bilateral meeting, Noda will "possibly exchange words with Hu for a short time", Kyodo said.

The agency said any summit could exacerbate differences over the islands.

Noda also plans to skip a one-on-one meeting with South Korean President Lee Myung-Bak because Tokyo and Seoul are at odds over a different set of disputed islands, known as Takeshima to Japanese and Dokdo to Koreans, Kyodo said.

A Japanese foreign ministry official said Noda's schedule in Vladivostok was still being finalised.

The Department of Foreign Affairs said in a statement that China's recent assurance could have positive or negative connotations for the Philippines, which has territorial disputes with China.

The statement came after China's Foreign Minister Yang Jiechi told US Secretary of State Hillary Clinton that "freedom and safety of navigation in the South China Sea is assured", at a rare joint news conference in Beijing on Wednesday.

However the Philippines said Yang's statement may mean that China is "making it appear that it is the sole guarantor of freedom of navigation", in the hotly-disputed South China Sea.

"What if China refuses or withdraws such assurance? Does that mean that the freedom of navigation does not exist in the (South China Sea?) We wish to seek a clarification on this," the department added.

The Philippines said freedom of navigation was a right under international law and expressed hopes that China's new statement showed it would now abide by international law.

The statement also reaffirmed the Philippines' objections to China's claim over most of the South China Sea, a mineral and fish-rich region that is also among the world's busiest sea passages.

The Philippines has in recent months accused China of "duplicity" and "intimidation" in pressing its claims to territory in the South China Sea.

Several other Southeast Asian countries also have conflicting claims with China over the area.

Tensions between the two countries rose after Philippine and Chinese ships began a stand-off in April over the Scarborough Shoal, an rocky outcrop in the South China Sea.

China claims the shoal as well as nearly all of the South China Sea, even waters close to the coasts of neighbouring countries. The Philippines says the shoal is well within its 200-nautical-mile exclusive economic zone.