China has warned that Japanese campaigners' claims to the Diaoyu Islands threaten to strain relations with Tokyo. The Foreign Ministry yesterday denounced two Okinawa protesters who staged a 45-minute landing on the disputed East China Sea islands, saying China's centuries-old claim to the chain was 'clear and consistent'. Ministry spokesman Cui Tiankai said: 'Since ancient times, the Diaoyu Islands have belonged to China. 'We demand the Japanese Government take measures to prevent this violation of China's sovereignty from harming Sino-Japanese relations once again.' Japanese authorities earlier rebuked the protesters - a reporter and a municipal assemblyman - for landing on the rocky islands, in what Tokyo described as a 'regrettable thing'. Beijing acknowledged Japan's regret, but warned it would not tolerate any similar exploits. 'We note there is a conflict on this issue,' Mr Cui said. 'We maintain this issue can be solved through dialogue at the proper time.' The Foreign Ministry refused to comment when asked if China would use force to stake its claim to the islands, believed to be near oil reserves.