Iranian Ayatollah Ali Khamenei gestures before delivering a speech in Mashad, Iran, March 21, 2018. Photo: Leader.ir / Handout via Reuters.

Any move to negotiate with Israel would be an “unforgivable mistake,” Iranian Ayatollah Ali Khamenei said on Wednesday, after Saudi Arabia’s crown prince said Israelis were entitled to live peacefully on their own land.

Saudi Arabia — birthplace of Islam and site of its holiest shrines — does not officially recognize Israel, but Mohammed bin Salman’s comments, quoted in the US magazine The Atlantic, are a further sign of an apparent thawing in bilateral ties.

They come as mainly Sunni Muslim Saudi Arabia faces off against Shi’ite Iran in a regional power struggle. Tehran and Riyadh back opposing sides in the conflicts in Yemen and Syria as well as rival political groups in Iraq and Lebanon.

“Movement toward negotiation with the cheating, lying and oppressive regime (of Israel) is a big, unforgivable mistake that will push back the victory of the people of Palestine,” Khamenei said in a statement posted on his official website.

The statement, which did not explicitly name Saudi Arabia, said it was the duty of all Muslims to support Palestinian “resistance” movements and it pledged continued Iranian backing for the Palestinian Islamist group Hamas.

After the crown prince’s comments, his father King Salman reiterated Saudi Arabia’s support for a Palestinian state.

Riyadh has long maintained that normalizing ties with Israel hinges on an Israeli withdrawal from lands captured in the 1967 Six-Day War that Palestinians seek for a future state.

However, Saudi Arabia opened its air space for the first time to a commercial flight to Israel last month, which an Israeli official hailed as historic following two years of efforts.

In November, an Israeli cabinet member disclosed covert contacts with Saudi Arabia, a rare acknowledgment of long-rumored secret dealings which Riyadh still denies.