Former military chief of staff Benny Gantz said Wednesday that he could not form Israel’s next government, prolonging the country's political uncertainty after deadlocked elections in September.

"Returning the mandate" to President Reuven Rivlin raises the prospect of Israel holding its third national election in a year. There are now 21 days in which any member of Parliament can become prime minister if they muster the 61 signatures needed to achieve a majority in the Knesset.

Prime Minister Benjamin Netanyahu failed to form a government last month, after which the mandate was transferred to Gantz.

"Gantz informed Rivlin that he will continue his efforts over the next 21 days to form a good government for the citizens of Israel," a spokesperson for his centrist Blue and White party told NBC News hours before the deadline for him to gather enough support.

"Gantz thanked Rivlin for his support in the process and asked that he continue to provide assistance down the road."

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Wednesday's announcement followed weeks of negotiations between the two leaders. Gantz had refused to enter a unity government that would keep Netanyahu in power while corruption charges loomed against him.

Netanyahu, dubbed "King Bibi" by many for his decadelong dominance over Israeli politics, is waiting to see whether the country's attorney general will indict him on fraud and bribery charges in three corruption cases. He denies any wrongdoing.