JERUSALEM — The two main challengers to Israeli Prime Minister Benjamin Netanyahu announced an electoral alliance Thursday, posing a threat to the premier’s long tenure in office as he also faces potential corruption charges.

While earlier polls said Netanyahu looked likely to win the April 9 election, the combined power of his two main challengers from the political centre has shaken up the campaign.

An announcement by Israel’s attorney general ahead of polling day of charges against the prime ministers would greatly boost the new alliance’s cause, but it is unclear when a decision in the investigations will be unveiled.

Netanyahu has tacked further to the right as he faces the potential indictments and the challenge from the newly allied centrist politicians: Benny Gantz, a respected former armed forces chief of staff, and Yair Lapid.

He demonstrated that Wednesday by brokering a deal which could potentially see an extreme-right party win seats in parliament, leading critics to say he was pandering to "racists".

Gantz and Lapid have seized on such moves and the investigations to promote their alliance as one that can restore Israel’s values.

They said they had agreed to unite "out of a sense of deep national responsibility".

"The party will put forward a new leadership team which will guarantee the security of Israel and will reunite the divided elements of Israeli society," Lapid’s statement said.

At a joint address on Thursday evening Gantz decried Netanyahu’s rule as responsible for the "bad wind blowing in our streets, it is enough!"

"Instead of provocations we are proposing a national reconciliation," he said.

‘Choice is clear’

Other members of the alliance - to be called Blue and White, the colours of the Israeli flag - include two other ex-military chiefs of staff: Moshe Yaalon and Gabi Ashkenazi.

Gantz and Lapid plan to rotate as prime minister should they win.

Gantz would be premier for the first two-and-a-half years and Lapid, a former television journalist turned politician, would take over afterwards after first serving as foreign minister.

Netanyahu’s Likud party responded to the alliance by repeating the line of attack it has engaged in for weeks, seeking to label Gantz a "weak" leftist.

In a duelling address Thursday evening Netanyahu took aim at the new grouping and accused them of wanting to create a block with Arab Israeli deputies "who do not recognise Israel, and who instead want to destroy it".

"A Lapid-Gantz government would together with them create a Palestinian state that will extend to the suburbs of Tel Aviv," he said.

Israeli politics have moved firmly to the right in recent years, with much of the population having grown weary of calls for a two-state solution and unwilling to make signficant compromises in favour of the Palestinians.

Netanyahu already leads what is seen as the most right-wing government in Israel’s history.

Prominent members of his coalition openly rule out a Palestinian state and advocate annexing much of the occupied West Bank.

The 69-year-old leader’s political skills are well-known, and some analysts said even with a united opposition he would still be the clear favourite.

Netanyahu has been prime minister for around 13 years in all and would be on track to surpass founding father David Ben-Gurion as Israel’s longest-serving premier should he win in April.

He would not be required to step down if indicted, only after conviction with all appeals exhausted. He denies all allegations.

‘Centre versus right’

A poll released Thursday evening by private television channel 13 made troubling reading for the veteran premier, giving the Gantz-Lapid alliance 36 out of 120 seats in parliament and 26 for Likud.

Shmuel Sandler, political science professor at Bar Ilan University, said the merger sharpened the focus of the race.

"It’s going to be centre versus right," he said.

"I think given the current polls, Netanyahu still has a better chance of winning even after the merger."

A campaign that has already turned into a mud-slinging fest is meanwhile likely to become dirtier.

Gantz had at first sought to remain above the fray, but he unleashed a stinging rebuke of Netanyahu in a Tuesday speech, accusing him of becoming "addicted to the pleasures of power, corruption and hedonism".

"When I lay in muddy foxholes with my soldiers on frozen winter nights, you, Benjamin Netanyahu, left Israel to improve your English and practice it at luxurious cocktail parties," Gantz said.

Netanyahu struck back immediately, highlighting his own military experience and arguing that his English oratory has benefited Israel.

"Benny Gantz, be ashamed of yourself," the prime minister said in a video clip, saying he had "risked my life time and time again for our country". — AFP