A rise in radiation halted the clean-up of radioactive water at Japan's Fukushima nuclear power station on Saturday, June 18, hours after it got under way, a fresh setback to efforts to restore control over the quake-stricken plant, Reuters reports.

Tokyo Electric Power Company, the operator of the Fukushima Daiichi plant, said it expected to resume the clean-up within a week.

A statement issued by the utility, known as Tepco, said the suspension was prompted by a faster than expected rise in radiation in a part of the system intended to absorb caesium.

"At the moment, we haven't specified the reason," a Tepco spokesman told a news conference. "So we can't say when we can resume the operation. But I'd say it's not something that would take weeks."

The official said teams working at the plant believed the radiation rise could be linked either to sludge flowing into the machinery absorbing caesium or a monitoring error caused by nearby pipes carrying contaminated water.

But a resumption, he said, was critical to deal with the highly radioactive water. Officials say 110,000 tons, the equivalent of 40 Olympic swimming pools - is stored at the plant, 240 km (150 miles) northeast of Tokyo.

"Unless we can resume the operation within a week, we will have problems in disposing of the contaminated water," the official said. "But if this is caused by the reasons we are thinking, we can resume the operation within a week."

The official said Tepco for the moment foresaw no delay in its overall plan to bring the Fukushima Daiichi plant fully under control by the end of the year.

The plan, derided by some critics as too optimistic, calls for a shutdown of its three unstable reactors by January 2012.