By Rebecca Ballhaus in Washington and Sune Engel Rasmussen in Beirut 

President Trump on Tuesday threatened a heavy military response against Iran in the event of an attack, a day after he imposed sanctions that aim to freeze the assets of Supreme Leader Ali Khamenei's office and several Iranian military commanders

"Any attack by Iran on anything American will be met with great and overwhelming force," Mr. Trump tweeted. "In some areas, overwhelming will mean obliteration."

Mr. Trump's tweets ratcheted back up tensions between Washington and Tehran that have oscillated in recent days since Iran downed a U.S. military drone last week. The president initially suggested he didn't believe the downing of the drone was intentional, but he later ordered retaliatory strikes in Iran -- only to abandon them, saying estimates provided to him showed as many as 150 people could have been killed.

Earlier Tuesday, Iran said the new U.S. sanctions closed the door on diplomacy and threatened global stability. Iranian President Hassan Rouhani called the sanctions "outrageous and stupid" and said it was "obvious" that the U.S. was lying about wanting to negotiate with Iran.

White House national security adviser John Bolton, in Jerusalem for a rare gathering of his Israeli and Russian counterparts, called on Iran to negotiate a new, broader agreement to supersede the 2015 nuclear deal, which the Trump administration withdrew from in May 2018 and imposed a crippling round of sanctions on Iranian industries and organizations.

"The president has held the door open to real negotiations that completely and verifiably end Iran's nuclear weapons program, its pursuit of ballistic missile delivery systems and support for international terrorism and its other malign behavior world-wide. All that Iran needs to do is walk through that open door," Mr. Bolton said. He rejected Iranian demands that sanctions be lifted as a condition of talks, saying Tehran would "either get the point" from current restrictions, or "we will simply enhance the maximum pressure campaign further."

Secretary of State Mike Pompeo, visiting Kabul on Tuesday, said Mr. Rouhani's comments on diplomacy with the U.S. were "a bit immature and childish." He said the Trump administration would "remain steadfast" in its effort to deter Iran, including the economic-pressure campaign against the regime.

Mr. Trump said the sanctions he imposed would deny access to global financial resources for Mr. Khamenei and others. His administration also plans to target Iranian Foreign Minister Javad Zarif later this week.

The U.S. and Israel see Russia as a key mediator to help in a campaign against Iran. Russia and Iran helped Syrian President Bashar al-Assad remain in power through a brutal civil war, but cracks in their partnership have begun to show, as the two countries vie for power in a postconflict Syria.

Russian national security adviser Nikolai Patrushev said Iran and Russia "can influence each other and listen to each other." But he stopped short of committing to removing Iran's presence in Syria, where Tehran has funded and trained militias that Israel sees as an urgent national-security threat.

"We are aware of Israel's concerns and hope the threats will be removed so that Israel will be safe," Mr. Patrushev said. "But we also need to remember the interest of other regional powers. Should we ignore them, we won't achieve concrete results."

Meanwhile European governments are ready to use a special purpose vehicle that seeks to maintain commerce with Iran, European Union foreign policy chief Federica Mogherini said Tuesday.

Ms. Mogherini said she hoped the implementation of the long-promised trade mechanism would help persuade Iran not to press ahead with threatened steps to disregard some limits imposed by the 2015 Iranian nuclear deal.

Iran's foreign ministry echoed Mr. Rouhani, saying Washington signaled it wasn't genuine about wanting to talk to Tehran because it is sanctioning Iran's most senior diplomat.

"The useless sanctions against Iran's leader and the commander of diplomacy means the permanent closure of the channel of diplomacy with the desperate U.S. administration," foreign ministry spokesman Abbas Mousavi said on Twitter.

"The Trump administration is destroying all the customary, international mechanisms for preserving global peace and security."

Hesameddin Ashena, a top aide to President Rouhani, said sanctions on Mr. Zarif would turn the foreign minister into "Iran's Mandela."

"He fought against domestic apartheid," Mr. Ashena said on Twitter, likely referring to Mr. Zarif's diplomatic efforts in bringing together disparate political factions in Iran, "and now he will fight international apartheid."

Aresu Eqbali in Tehran and Dov Lieber in Jerusalem contributed to this article.

Write to Rebecca Ballhaus at Rebecca.Ballhaus@wsj.com and Sune Engel Rasmussen at sune.rasmussen@wsj.com

(END) Dow Jones Newswires

June 25, 2019 11:51 ET (15:51 GMT)