WASHINGTON - Mark Bowman on Capitol Hill contributed to this report.

WHITE HOUSE - U.S. President Donald Trump is ratcheting up his threats against Iran, saying an attack by Tehran on "anything American" would "be met with great and overwhelming force" - adding that in some instances, "overwhelming will mean obliteration."

In a series of Tuesday morning tweets, Trump dismissed as "very ignorant and insulting" Iran's statement hours earlier saying it was ending the possibility of diplomatic talks with the U.S.

The statement from Tehran was issued after Trump stiffened economic sanctions the previous day against the Islamic republic, specifically targeting the country's supreme leader, Ayatollah Ali Khamenei.

An Iranian government official is quoted saying that sanctions on Khamenei equal an attack on the nation.

Trump also cast aspersions on two U.S. political figures, saying, "No more John Kerry & Obama!" again rejecting the international pact negotiated by former Secretary of State Kerry and former President Barack Obama to restrain Iran's nuclear weapons development.

Trump withdrew from the 2015 agreement last year and reimposed sanctions aimed at debilitating Iran's economy in an effort to force it to engage in one-on-one nuclear negotiations with the U.S.

The U.S. says it could also add sanctions targeting Iranian Foreign Minister Mohammad Javad Zarif, but Iranian President Hassan Rouhani, in a televised address, said, "You sanction the foreign minister simultaneously with a request for talks?"

Shortly prior to Trump's tweets, Iran's foreign ministry spokesman, Abbas Mousavi, tweeted that sanctions on Khamenei and Zarif would mean "the permanent closure of the path of diplomacy."

On the floor of the U.S. Senate on Tuesday morning, minority leader Chuck Schumer termed the tension between Washington and Tehran "a dangerous situation," adding, "Even if the president doesn't intend war, his erratic, inconsistent and off-the-cuff policies could lead us to bumble into war."

Senate Majority Leader Mitch McConnell defended the president and criticized opposition Democrats "afflicted by Trump derangement syndrome that they repeat Iranian talking points and advertise the absurd notion that our country, our administration, our president are somehow to blame for Tehran's violent aggression."

The Republican senator added, "Clearly the president wants to avoid war, hence the deliberate and judicious approach he has taken since the shootdown" last week of a U.S. Navy drone by Iran.

Trump has called the new sanctions order a "strong and proportionate" U.S. response to the downing of the un-manned U.S. military aircraft, which Washington says occurred in international airspace near the Strait of Hormuz, and Iran claims occurred over its airspace.

The U.S. leader said he imposed the sanctions because of a series of "belligerent acts" carried out by Iran, which U.S. officials say include Iran's targeting of Norwegian and Japanese ships traversing the Strait of Hormuz with mine explosions days before the attack on the drone.

U.S. National Security Advisor John Bolton said during a visit to Jerusalem on Tuesday that Trump "has held the door open to real negotiations," and Iran has responded with what he called "deafening silence."

Iran has repeatedly denied it was working to develop nuclear weapons, and the U.N. nuclear watchdog charged with monitoring the 2015 agreement has certified Iran is in compliance with the terms of the deal.

As the Trump administration has increased pressure on Tehran in recent months, and as Iran has complained that the other signatories to the nuclear deal have not done enough to help it maneuver around the U.S. sanctions, Iranian officials have pledged to stop abiding by some certain restrictions it had agreed to, such as the amount of highly enriched uranium it can have.