Israel’s Opposition leader Isaac Herzog has upped the ante in coalition talks, telling Prime Minister Benjamin Netanyahu to stop holding “parallel negotiations” with ultra-nationalists.

Herzog, who could become foreign minister if he joins Benjamin Netanyahu’s right-wing government, was reacting to reports that the prime minister was also courting Avigdor Lieberman, who wants to become defence minister. 

“Until Netanyahu decides where he is going, we will not conduct parallel negotiations,” said Herzog. “If Netanyahu wants to bring Lieberman into the government, let him do it.”

Herzog currently heads the Zionist Union, an amalgamation of the Labor Party and Tzipi Livni’s Hatnua, but talk of him joining the ruling coalition has angered colleagues, including former Labor leader Shelley Yachimovich, who likened Netanyahu’s overtures to “throwing a dog a bone”. 

On Sunday, Herzog said joining the coaltion government would be a “rare” opportunity, but his tone has since hardened, and he ruled out working alongside Lieberman, who has previously supported the population transfer of Israel’s Arabs out of Israel, and has most recently demanded the death penalty for Palestinians who attack Israelis. 

Elsewhere, Herzog, said he felt there was an opportunity to reach a peace settlement with the Palestinian leadership, and praised comments this week from Egyptian autocrat Abdel Fattah al-Sisi, who is backing a French conference initiative to reinvigorate the stunted peace process. 

In a speech, al-Sisi promised improved relations with Israel if the two sides seized a “realistic” and “great” opportunity to reach a lasting peace agreement.