"We have lodged a stern protest and reaffirmed our stance that the Diaoyu islands are part of our territory," the foreign ministry said.

According to the ministry, Tokyo unveiled Japanese names for the four islets in the Diaoyu island chain, known as Senkaku in Japan, on Friday.

Japan has said it plans to finish naming 39 uninhabited islands by the end of March, including some near the archipelago.

The islands, which are believed to be surrounded by oil and gas reserves, have long been a source of friction between Japan, Taiwan and China, which also claims sovereignty of the territory.

There have been a number of standoffs in recent years between Japanese patrol craft and Taiwan's anti-Japan activists trying to sail to the disputed area to press Taipei's claim.

Japan officially recognises China rather than Taiwan but maintains close trade ties with the island.