Japan’s four mobile operators said on Tuesday a joint study they conducted found no evidence that radio waves from mobile phones harm body cells or damage DNA in contrast to findings from a similar study in Europe.

NTT DoCoMo Inc., KDDI Corp., Vodafone K.K., and Tu-Ka Cellular Tokyo Inc. said they had studied the effect of radio waves on human cells for over two years and found no damage even though they used radio waves up to 10 times stronger than normally used.

The interim results come after researchers in Europe announced opposite findings in December and could further cloud the debate over the effect of mobile phones on health.

The Japanese study’s findings will be announced at the Bioelectromagnetics (BEMS) annual meeting in June. Results have also been submitted to the BEMS Journal, the companies said.

The $100 billion a year mobile phone industry asserts that there is no conclusive evidence that electromagnetic radiation causes harm.

About 730 million mobile phones are expected to be sold to consumers this year, and nearly 2 billion people around the world use one.

The research project was started in response to a World Health Organization (WHO) recommendation to further study the safety of radio waves from mobile phones and base stations.

The four-year study funded by the European Union and coordinated by German institute Verum found human and animal cells exposed to electromagnetic fields typical of mobile phones were damaged and could not always be repaired.

Other independent studies into the health effects of mobile phone radiation have found it may have some effect on the human body, such as heating up the brain and causing headaches.

A study by the International Agency for Research on Cancer is expected to announce results in late 2005 at the earliest. A separate study by WHO is expected a year later.

The Japanese companies said they planned to continue their research and publish further results.

Vodafone K.K. is a unit of Britain’s Vodafone Group Plc . Tu-Ka is a unit KDDI.