YINCHUAN - Chinese Vice Premier Li Keqiang told visiting Papua New Guinea Prime Minister Peter O'Neill on Tuesday that the Japanese government's deal to "purchase" the Diaoyu Islands from the so-called "owner" severely undermines China's territorial sovereignty.

"The Chinese side has lodged solemn representations and strong protest to the Japanese government," Li said as he met with O'Neill in Yinchuan, capital of northwest China's Ningxia Hui autonomous region. O'Neill was here to attend the China (Ningxia) International Investment and Trade Fair and the 3rd China-Arab States Economic and Trade Forum.

The Diaoyu Islands and their affiliated islets have been an inherent part of China's territory since ancient times, and China has indisputable sovereignty over them, Li said.

Highlighting China's firm resolution and will to safeguard its national sovereignty and territorial integrity, the vice premier vowed "we will maintain our sovereignty over the Diaoyu Islands resolutely."

"Both China and Papua New Guinea were victims to the Japanese fascist invasion back in the Second World War," Li reminded his visitor, adding that Japan's position today on the issue of the Diaoyu Islands is an outright denial of the outcomes of victory in the war against fascism and constitutes a grave challenge to the post-war international order.

No nation or people who are peace-loving and justice-upholding will tolerate Japan's stance, according to Li.

Echoing the Chinese vice premier, O'Neill said Papua New Guinea understands China's stance and that Japan's move cannot be accepted by the international community.

The international community should work together to defend the post-war world order, O'Neill added.