Iran's Supreme Leader Ayatollah Ali Khamenei called Wednesday on the people of Muslim countries to defeat Israel. "With an intense and planned struggle, they should force the enemy to retreat toward the point of demise," he said.
Any move to negotiate with Israel would be an "unforgivable mistake", the cleric added, after Saudi Arabia's crown prince said Israelis were entitled to live peacefully on their own land.
Supreme Leader Khamenei later tweeted, "On days when escalation of oppression & barbarism by the Zionists, in Gaza has saddened and angered those who care for Palestine, we reiterate the perpetual stance of the Islamic Republic regarding the issue of Palestine.
"The return of dignity and power to the Islamic nation is exclusively linked to resistance—while confronting arrogant powers and their wicked plots—and the issue of Palestine is at the top of Islam's international agenda in the face of the arrogant front."
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 Shiite 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 Arab lands captured in the 1967 Six Day War—territory 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 that Riyadh still denies.
Khamenei issued Wednesday's statement in reply to a letter he recently received from Hamas chief Ismail Haniyeh that criticized the support of Arab governments in the region for the United States.