Researchers estimated that youngsters living within 200 meters (yards) of the lines were about 70 percent more likely to develop leukemia compared to those who lived beyond 600 meters, the UK's Press Association reported.

Those living between 200 and 600 meters of the high-voltage pylons had around a 20 percent increased risk.

But the researchers said they had not been able to show that the power lines were the cause of the increased risk and admitted there was possibility their findings could be due to chance.

Some researchers have suggested that low frequency magnetic fields, such as those caused by the production of electricity, could possibly be linked to cancer.

However other studies, such as the large UK Childhood Cancer Study (UKCCS) which reported its results recently, have disputed this risk.

The latest study, published in the British Medical Journal, looked at more than 29,000 children with cancer, including 9,700 with leukemia, born between 1962 and 1995, and a control group of healthy youngsters in England and Wales.

Dr. Gerald Draper and colleagues from the Childhood Cancer Research Group at Oxford University, and Dr. John Swanson, a scientific adviser at National Grid Transco, measured the distance from children's home addresses at birth from the nearest high-voltage power line.

They found that 64 children with leukemia lived within 200 meters of the line, while 258 lived between 200-600 meters away.

Putting the risks into perspective, the researchers said that about five of the 400-420 cases of childhood leukemia that occur each year in England and Wales may be linked to power lines.

They did not find any increased risk for other types of childhood cancer.

The researchers also only measured distance from power lines, and not the magnetic field from either the power lines or other sources.

Draper said they were unable to say that power lines were the cause of the increased risk found and the magnetic fields were unlikely to be involved.

"It may not be the effect of power lines at all. It may be something to do with the kind of areas where power lines are located, or the sort of people who live in these areas and we will be looking at that further," he said.

The researcher said that children from more well-off families and those living in less densely populated areas appeared to be at a slightly higher risk of leukemia, and that these were population characteristics that needed to be investigated further.

Draper also said their results could be chance findings, although in statistical terms they were still significant.

But he said chance could not be ruled out because they were unable to say what the actual cause of the increased risk was.

Swanson said the electricity industry was determined to get to the truth behind theories about links to childhood leukemia and as a responsible industry was pleased to be part of this study.

"We have strengthened the evidence that something is happening, but we haven't made any connection about why it is happening, if only we had," he said.

Draper said it would be wrong to make recommendations about where people should live based on their findings until there was more explanation for the results.

However he said based on previous research he would be unhappy moving into a house where there were electromagnetic field exposures of 0.4 microtesla or higher.

Swanson said if he had found the perfect house he would not let proximity to power lines deter him from moving in, but if all things were equal and another property was further away he would find that preferable.

The UKCCS reported last month that most cases of childhood leukemia had their origins before birth and may be triggered by infections early in life.

It said there was minimal risk of childhood cancer from electrical installations or magnetic field levels.

But Eddie O'Gorman, chairman of the charity Children with Leukemia, said: "We have to do everything we can to protect young lives -- there is now a clear case for immediate government action.

"Planning controls must be introduced to stop houses and schools being built close to high voltage overhead power lines."

A Department of Health spokeswoman said they realized this was an important issue which had caused anxiety.

"We have been closely following developments in this area for many years and have already taken action by setting up a group of experts especially to consider whether there is any need to develop precautionary measures to reduce exposures to electromagnetic fields," the spokeswoman said.