China has warned Japan to stop an "illegal" trip to disputed islands in the East China Sea as Japanese politicians prepared to set sail.

The Chinese foreign ministry said the proposed visit would undermine its "territorial sovereignty".

It is the latest move in an escalating dispute over the islands, known as Senkaku in Japan and Diaoyu in China.

On Friday, Japan which controls the islands, deported several Chinese activists who landed there this week.

The islands, which Taiwan also claims, are close to strategically important shipping lanes, offer rich fishing grounds and are thought to contain oil deposits.