Former Japanese Prime Minister Naoto Kan is to testify before a parliamentary commission into the Fukushima disaster on his handling of the crisis, which began in March 2011.
Questioning is expected to focus on Mr Kan’s response in the hours and days after tsunami damage tipped three nuclear reactors into meltdowns.
The panel has already heard from lawmakers and nuclear industry experts.
The commission is due to deliver its report in June.
On Sunday, Trade and Industry Minister Yukio Edano - who was the top government spokesman at the time - told the commission there had been no attempt to mislead the public about the severity of the crisis.
He said the government had not fully understood the extent of the damage to the plant.
He also said that Japan had refused a US request to place its nuclear experts in the prime minister’s office, citing sovereignty issues.
Fuel pond fears
Naoto Kan is expected to face questions on his early efforts to contain the crisis.
He has been criticised for being hesitant to take emergency powers into his hands at first and then for interfering too much, says the BBC’s Roland Buerk in Tokyo.
A breakdown of trust between Mr Kan, bureaucrats and the plant’s operator Tepco is said to have hampered the operation, our correspondent adds.
At the Fukushima Daiichi plant itself, the reactors are now stable, Tepco says.
But there is concern about the spent fuel pool on the top floor of the badly damaged reactor number four building.
If it collapses, it could cause another catastrophe, officials have warned. But Tepco says it has reinforced the structure against another earthquake.
Meanwhile, tens of thousands of residents remain evacuated from an exclusion zone around the plant.
