TOKYO - Japan's ambassador to China returned to Beijing on Monday after Tokyo summoned him over the weekend to discuss the escalating tension over the Diaoyu Islands.

Foreign Minister Koichiro Gemba denied that the summoning of the ambassador, Uichiro Niwa, was meant as a protest to Beijing after Chinese patrol boats entered disputed waters near the islands, a ministry spokesman said.

Last week, the Chinese vessels twice entered waters near the islands, after Japanese Prime Minister Yoshihiko Noda said that Japan could buy the island from their private owners, instead of letting Tokyo governor Shintaro Ishihara go ahead with a similar plan.

Niwa, a former president of trading firm Itochu Corp, last month said he opposed Ishihara's plan, angering conservatives and drawing fire from the Foreign Ministry.