Israeli Prime Minister Benjamin Netanyahu's main political rival, former military chief Benny Gantz, has received an official mandate from Israel's president to try to form the country's next government.

"I give you my word, I will do all in my ability to establish within a few days as broad and patriotic a government as possible," Mr Gantz, leader of the centrist Blue and White party, said in a ceremony next to Israeli President Reuven Rivlin.

Mr Gantz has the support of 61 of parliament's 120 legislators.

However, the path to unseating Mr Netanyahu could still prove difficult, and a unity government with the veteran leader has been widely mooted.