The Financial Services Agency is likely to order the Tokyo Stock Exchange to report on the cause of its worst-ever system glitch that caused the bourse to suspend Thursday's trading, sources close to the matter said.

It is "very regrettable," the government's top spokesman, Chief Cabinet Secretary Katsunobu Kato, told a press conference in reference to the largest outage for the exchange since it fully computerized the system in 1999.

The financial watchdog issued business improvement orders to the TSE in 2005 and 2012 when the bourse partly suspended trading due to system malfunctions.

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Tokyo stock trading halted entire Thurs. session due to system glitch