Israel’s centre-left opposition alliance has broken up in a dramatic realignment of the country’s political battleground just months from a general election.

Avi Gabbay, the leader of a coalition of opposition parties, made the unexpected announcement live on television that he would no longer partner with veteran politician Tzipi Livni, even as she sat expressionless next to him. It was not clear if Livni had been told of the move.

The now-defunct Zionist Union alliance, composed of Gabbay’s Labour and Livni’s Hatnuah parties, finished with the second highest number of seats in the last election in 2015.

With support from the more affluent districts around Tel Aviv and from liberal voters, the partnering had focused on unseating Benjamin Netanyahu’s rightwing Likud, but failed.

It has since tumbled in opinion polls and Gabbay, who took over as leader in 2017, has had an uneasy relationship with Livni, a former foreign minister.

“I still believe in partnership, in connections, in uniting a large camp committed to change, but successful connections necessitate friendship, upholding agreements and commitment to a course,” Gabbay told a meeting of Zionist Union parliament members. “That didn’t happen in this partnership.”

Livni spoke tersely afterwards, saying: “I’m not responding. I will make my decisions. Thank you,” before leaving the room. Apparently referring to earlier rumours of a potential spilt, she later tweeted that it was “good that the doubts had been dispelled”.

The disbandment follows a separate major shake-up among the ruling coalition. On Saturday, two rightwing cabinet ministers, Naftali Bennett and Ayelet Shaked, announced they were leaving their Jewish Home party to form a new one.

Polls show Netanyahu, who leads what is seen as the most rightwing administration in Israel’s history, is likely to win the 9 April polls. That would give him a fifth term in office and a good chance of succeeding the Jewish state’s founder, David Ben-Gurion, as the longest-serving prime minister.

Despite allegations of corruption, including police recommendations that he be indicted on charges of bribery and breach of trust in three separate cases, Netanyahu has held on to power through deals with ultra-nationalist secular and religious parties.

Last month, however, he called early elections, initially set for November, after internal divisions in the ruling coalition curbed his government’s ability to pass legislation. The prime minister, 69, now intends to form new alliances.

“I won’t intervene in how the left divides its votes,” he said in a statement after Gabbay’s announcement. “What’s important to me is that the right forms the next government too, and continues to lead Israel.”