Image copyright Reuters Image caption Tepco has struggled to store water contaminated by the plant

The operator of Japan's crippled Fukushima nuclear plant has begun work on a large underground ice wall to isolate toxic water it has produced.

The 1.5km (0.9 mile) wall will be made by inserting 1,550 pipes into the ground. Coolant circulating in the pipes will freeze the surrounding soil.

Some experts have expressed concerns over whether the project will work.

The plant experienced several leaks of radioactive water since being crippled by an earthquake and tsunami in 2011.

Last week, the Nuclear Regulation Authority agreed that plant operator Tepco could begin construction work on the frozen wall.

The government-funded ice wall is intended to stop nearby groundwater from seeping into the plant and mixing with contaminated water inside.

'Ambitious plan'

"We plan to end all the construction work in March 2015 before starting trial operations," a Tepco official said, adding that the ice wall could be operational months after construction.

The 2011 disaster knocked out cooling systems to the nuclear plant's reactors, three of which melted down.

Water is now being pumped in to cool the reactors, but storing the resultant large quantities of radioactive water has proved a challenge for Tepco.

Image copyright AFP Image caption Drilling works began on Monday to construct pipes to freeze the surrounding soil

The operator has also struggled to safely store groundwater that has mixed with the radioactive water and become contaminated.

Last month, Tepco began releasing groundwater into the sea after checking its radiation levels.

This is the latest and most ambitious plan to isolate and contain the nuclear disaster at Fukushima, the BBC's Rupert Wingfield-Hayes in Tokyo reports.

Nothing on this scale has ever been tried before, and keeping the ground frozen in an area with summer temperatures close to 40C may be very hard, our correspondent adds.

Some experts, including an American adviser assisting Japan with Fukushima clean-up efforts, have expressed doubts over whether the wall will work.