Iran's supreme leader formally endorsed Masoud Pezeshkian as the country's president on Sunday, after he won an election this month by pledging a pragmatic foreign policy and easing repression at home.

Pezeshkian, a relative moderate who will be sworn in on Tuesday, is taking office at a time of escalating Middle East tensions over the Israel-Hamas conflict in Gaza and Iran-backed Hezbollah in Lebanon.

Iran warned its arch foe Israel on Sunday against what it called any new adventure in Lebanon, after Israeli authorities blamed Hezbollah for a rocket attack on Saturday that hit a football ground in the Israeli-occupied Golan Heights killing 12 people, and vowed to inflict a heavy response.

Hezbollah denied any responsibility for the strike.

In a ceremony broadcast live on state television, Ayatollah Ali Khamenei gave his approval for Pezeshkian, and in a speech afterwards, the supreme leader reiterated Iran's longstanding anti-Israel stance.

"The Zionist regime (Israel) is not a state, it is a criminal gang, a bank of killers, and a terrorist band," Khamenei said in his speech, while praising the Palestinian Islamist group Hamas for its resistance against Israel in Gaza.

With the supreme leader calling the shots on all state matters, Pezeshkian is not expected to usher in major shifts on Iran's policies like Tehran's support for militia groups across the region.

The top authority in regional policy is not the president, but the powerful Revolutionary Guards, who answer only to Khamenei.

Pezeshkian's victory lifted hopes of a thaw in Iran's antagonistic relations with the West that might create openings for defusing its nuclear dispute with world powers.

But as the ultimate authority in Iran, Khamenei has the final say in all state matters like the country's foreign and nuclear policy as well as Pezeshkian's upcoming selections for key cabinet posts, such as the foreign, oil and intelligence ministers.

As the clerical establishment faces growing public discontent over economic hardships, Pezeshkian's top economic goal will be breaking free of the crippling U.S. sanctions, reimposed after Washington ditched Iran's 2015 nuclear deal with major powers.

"In response to global issues, we should act proactively and effectively ... priorities must be observed, today (on domestic front) the priority is economic issues," said Khamenei.

Pezeshkian is replacing hardline President Ebrahim Raisi, who was killed in a helicopter crash in May.