The head of the International Atomic Energy Agency (IAEA) team that will review Japan's decommissioning work at Fukushima Daiichi nuclear power plant this week, said on Monday (9 February) that contaminated water leakage remains a challenging issue.

Since the devastating March 2011 earthquake that caused triple meltdowns at the Fukushima plant, operator Tokyo Electric Power Co (Tepco) has struggled with the initial crisis and subsequent unprecedented work needed to decommission the facility.

The company floundered in dealing with several problems at the site, including a series of leaks of radioactive water into the Pacific Ocean.

Tepco proceeded with decommissioning steps, including the tricky removal of spent fuel rod assemblies from a badly damaged reactor building.

Dismantling the plant and decontaminating the nearby area is likely to take decades and cost ten of billions of dollars.

In January, Tepco said it would not be able to meet a self-imposed deadline to decontaminate water containing highly radioactive substances by the end of March.

The utility firm had proposed building a 1.4km underground wall of ice to block groundwater.

Tests began last month and Tepco hopes next year to begin construction - sinking giant refrigeration rods into the ground to create an impermeable wall of frozen earth.

"One of our objectives in this mission is to review up to what extent these countermeasures progressed, and the situation has been improved since 2013," said Juan Lentijo, IAEA director of the division of nuclear fuel cycle and waste technology.

The team of 15 experts will visit the Fukushima Daiichi site to observe the decommissioning work on Wednesday and release a report on 17 February.