As U.S. President Donald Trump prepares for his first presidential overseas trip to Israel, the Vatican, and Saudi Arabia, Tehran and Riyadh are accusing each other of being the main instigator of unrest in the Middle East.

Saudi Prince Muhammad bin Salman, defense minister and the designated heir to his father, King Salman, said in a rare televised interview on May 2 that he would not seek to open dialogue with Iran because Tehran’s goal is to dominate the Muslim world.

“The aim of the Iranian regime is to reach the focal point of Muslims (Mecca), and we will not stand idly by until the fight is inside Saudi Arabia,” bin Salman said. “We will work so that the battle is on their side, inside Iran, not in Saudi Arabia.”

Two days later, Iran’s ambassador to the United Nations, Gholamali Khoshroo, responded in a formal letter to the UN Security Council and Secretary-General Antonio Guterres. He lambasted Prince Muhammad’s remarks as “unlawful” and a “blatant threat,” and Saudi Arabia’s “unveiled admission to its complicity with terrorist groups inside Iran.”

“By these remarks, Saudi Arabia clearly admits its complicity in acts of terror and violence inside Iran, including the killing of nine border guards last month in southeast Iran,” Khoshroo said.

Khoshroo honed in on Prince Muhammad’s remarks on taking the battlefield into Iran.

“While categorically rejecting the baseless allegations against my country, I wish to underline that this statement reflects an explicit threat against the Islamic Republic of Iran and is a violation of Article 2 of the United Nations Charter, which requires all members to ‘refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state’,” he said.

A day before Prince Muhammad’s controversial remarks, Iranian Foreign Minister Mohammad Javad Zarif had tried to extend a conciliatory hand toward Riyadh.

“Islamic Republic has never rejected a mediation between Iran and Saudi Arabia,” he said.

Condemning the January 2016 attack on the Saudi Embassy in Tehran as “historic treason,” Zarif continued, “Conditions would be different today if this attack hadn’t happened.”

The attack intensified tensions between the two regional powers, already engaged at the time in proxy wars across the Middle East. Besides the wars in Syria and Yemen, they support political rivals in Bahrain, Iraq, and Lebanon.

Khoshroo said Saudi Arabia is the hand behind the creation of Al-Qaeda, the Islamic State, the Taliban, and the Al-Nusra Front, which is Al-Qaeda’s branch active in Syria. Despite its harsh take on Riyadh, Khoshroo’s letter was not completely devoid of conciliatory tones.

Iran has “no desire, nor any interest, in an escalation of tension in its neighborhood,” the letter emphasized. Khoshroo also said Iran is “ready for dialogue and accommodation to promote regional stability, combat destabilizing extremist violence, and reject sectarian hatred.”

“We hope Saudi Arabia will be persuaded to heed the call of reason,” the letter added.

The milder tone reflected previous comments by Iranian Foreign Ministry spokesman Bahram Qassemi. Echoing earlier statements by his boss, he announced Tehran was ready to normalize ties with Riyadh if Saudi Arabia halts its bombardment of Shi’ite rebels in Yemen.

Nevertheless, in his televised interview, Prince Muhammad ruled out Tehran’s proposal.

“Iran has never been honest in its dealings with Riyadh. Whatever Iranian officials say about rapprochement and mending relations is a piece of satire,” he said.

Earlier this year, Riyadh and Tehran resolved a contentious dispute by working out an agreement to allow Iranian pilgrims to attend the 2017 hajj. Iranians were largely absent from 2016’s hajj pilgrimage following a crowd stampede that killed hundreds of Iranian worshippers in 2015.

Otherwise, the atmosphere between Tehran and Riyadh has been increasingly strained. Saudi Arabia severed formal diplomatic relations with Iran in 2016 after Iranian protesters stormed the Saudi Embassy in Tehran venting anger over Riyadh’s execution of a prominent Shi’ite Muslim cleric.