WASHINGTON — US President Donald Trump said on Tuesday that he will withdraw the United States from the Iran nuclear deal, a landmark international agreement signed in 2015.

In a televised speech at the White House, Trump announced the exit, adding he will not sign the waiver of nuke-related sanctions against Iran, re-imposing sanctions lifted under the accord.

Moments later, UN Secretary-General Antonio Guterres voiced "deep concern" over Trump's decision to pull America out of the Iran nuclear deal.

"I am deeply concerned by today's announcement that the United States will be withdrawing from the Joint Comprehensive Plan of Action (JCPOA) and will begin reinstating US sanctions (against Iran)," said Guterres in a statement, using the official name of the July 2015 agreement between Iran and the six world powers of Britain, China, France, Germany, Russia and the United States.

"I call on other JCPOA participants to abide fully by their respective commitments under the JCPOA and on all other (UN) member states to support this agreement," said Guterres.

Iran's President Hassan Rouhani said Tuesday that the Islamic republic will remain in the nuclear deal with other signatories of the JCPOA without the United States.

"From this time on, the nuclear deal is an accord between Iran and five countries," Rouhani said in live speech broadcast from state TV.

Iran proved that it has been committed to its international obligations, Rouhani said, adding that "our experience shows that over the past 40 years the United States has never been reliable vis-a-vis its commitments."

In his Tuesday speech, Trump repeated his tough stance on the deal, or the JCPOA, saying it had failed to prevent Iran from developing nuclear weapons or supporting terrorism in the region.

The JCPOA "allowed Iran to continue enriching uranium" and "lifted crippling economic sanctions" on Iran in exchange for "very weak limits" on its nuclear activity, "and no limits at all on its other malign behavior," he said.

"The United States will withdraw from the Iran nuclear deal" and impose "the highest level" of economic sanctions on Tehran, he said.

At the end of his remarks, he signed a presidential memorandum to begin reinstating US nuclear sanctions on the Iran.

After Trump's speech, the White House said in an emailed message to the media that Trump has "directed his administration to immediately begin the process of re-imposing sanctions related to the JCPOA," and "the re-imposed sanctions will target critical sectors of Iran's economy, such as its energy, petrochemical, and financial sectors."

"Those doing business in Iran will be provided a period of time to allow them to wind down operations in or business involving Iran," it added. "Those who fail to wind down such activities with Iran by the end of the period will risk severe consequences."

US Secretary of the Treasury Steven Mnuchin said in an announcement that "Treasury's Office of Foreign Assets Control (OFAC) is taking immediate action to implement the President's decision."

Meanwhile, US Secretary of State Mike Pompeo said in a statement that the United States "will be working with our allies to find a real, comprehensive, and lasting solution to the Iranian threat."

Trump also said after his speech that Pompeo is on the way to the Democratic People's Republic of Korea (DPRK) to prepare for his meeting with the country's top leader Kim Jong Un.

In response, former US President Barack Obama, whose administration brokered the deal, said in a Facebook post Trump's announcement is "so misguided" and "a serious mistake."

"The JCPOA is working," Obama said, adding that "the United States could eventually be left with a losing choice between a nuclear-armed Iran or another war in the Middle East" without the landmark deal.