The Vatican's top diplomat warned on Wednesday that the ongoing U.S.-Israeli attacks on Iran undermine international law and said nations do not have a right to launch "preventive wars", in an unusually direct criticism of the military campaign.

"If states were to be recognised as having a right to 'preventive war' … the entire world could risk going up in flames," Cardinal Pietro Parolin, the Vatican's Secretary of State, said in an interview with Vatican News.

Asked about the U.S.-Israeli strikes, which have pressed on for the fifth day, Parolin said they had caused a "weakening of international law (that) is truly alarming".

"The rule of force has replaced the force of law, with the conviction that peace can arise only after the enemy has been annihilated," the cardinal told the Vatican's media outlet.

It is unusual for Vatican diplomats to openly critique specific military campaigns. Vatican officials usually prefer to avoid press coverage and operate behind the scenes, leaving open the possibility of the Church serving as mediator in conflicts.

U.S. President Donald Trump has said the strikes against Iran were needed to prevent the country from developing a nuclear weapon, which Tehran denies seeking, and to thwart its long-range ballistic missile program.

Parolin, the Vatican's lead diplomat since 2013 and a front-runner in the 2025 conclave of cardinals that eventually elected Pope Leo, is known as someone who is usually very cautious with words.

Leo did not address the ongoing conflict in his weekly audience on Wednesday with pilgrims in St. Peter's Square.

The pope made an impassioned appeal on Sunday for an end to the conflict. He called for a stop what he termed a "spiral of violence".