By Mari Saito

TOKYO (Reuters) - Japanese Prime Minister Shinzo Abe ordered the scrapping of two Fukushima nuclear reactors that survived the 2011 tsunami, a write-off that threatens to complicate a turnaround plan the operator has presented to creditors.

He also said he stood by his commitments to the International Olympic Committee of insuring a safe 2020 Summer Games.

"I will work hard to counter rumours questioning the safety of the Fukushima plant," he said.

Abe, speaking to reporters after a tour of the plant on Thursday, said he told Tokyo Electric Power Co to set a time frame for dealing with leaking contaminated water.

"In order for them to concentrate on this, I have directed them to decommission the No. 5 and No. 6 reactors that are now halted," Abe said.

A tsunami crashed into the Fukushima Daiichi plant on March 11, 2011, causing fuel-rod meltdowns, radioactive contamination of air, sea and food and triggering the evacuation of 160,000 people in the world's worst nuclear accident since Chernobyl in 1986.

More recently, authorities have been struggling to contain leaks of radioactive groundwater.

Tokyo Electric president Naomi Hirose promised that the company will make a decision on the decommissioning of the two reactors within the year, Abe said.

Abe's visit to the plant, 240 km (140 miles) north of Tokyo, came after he pledged that the government would take a more central role in the clean-up as part of Tokyo's successful bid for the Olympics.

Four reactors were destroyed by meltdowns and hydrogen explosions. The No. 5 and No. 6 reactors escaped serious damage and Tokyo Electric has been allowed to carry the facilities as an asset on its balance sheet.

Tokyo Electric, which has posted more than $27 billion in net losses since the disaster, is negotiating with a syndicate of Japanese banks for a refinancing of 80 billion yen ($816 million) due next month.

As of April, the company listed 745.5 billion yen ($7.5 billion) in nuclear power generation assets. Those included the No. 5 and No. 6 reactors as well as the utility's Fukushima Daini nuclear plant and Kashiwazaki Kariwa - the world's largest nuclear plant - in northern Japan.

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Both of those other two plants are now halted and it is uncertain whether they can be restarted in the face of local opposition.

Abe said Hirose promised to finish treating contaminated water at Fukushima by March 2015.

(Reporting by Mari Saito, Kiyoshi Takenaka and Elaine Lies; Editing by Nick Macfie)