U.S. President Donald Trump (Xinhua file photo)

WASHINGTON, Jan. 12 (Xinhua) -- U.S. President Donald Trump on Friday said he will extend sanctions relief on Iran under a landmark nuclear deal for the last time, threatening a U.S. withdrawal from the pact if the U.S. Congress and his European allies can not fix the alleged "disastrous flaws."

Trump's latest move casts doubt on the future of the deal that was signed in 2015 between Iran, the P5+1 - Russia, France, China, Britain, the United States, plus Germany - and the European Union, a successful practice of solving a hot spot issue through political and diplomatic means.

LAST CHANCE OR DESPERATE ATTEMPT

In a White House statement, Trump called the waiver a "last chance" to fix the "flaws" of the Iran nuclear deal.

"The United States will not again waive sanctions in order to stay in the Iran nuclear deal," unless it gets the agreement it wants, added Trump.

In a tweet following Trump's harsh stance, Iranian Foreign Minister Mohammad Javad Zarif said Friday that it was a "desperate attempt" to undermine an accord which Iran insisted was "not renegotiable."

Trump has been criticizing the nuclear deal since it was signed in 2015, which has been widely seen as providing "clear and tangible" benefits by limiting Iran's nuclear program.

Last October, Trump decertified to Congress Iran's compliance with the pact, regardless of reports provided by the International Atomic Energy Agency, the international non-proliferation watchdog, confirming that Tehran has been in full compliance with the deal.

The United States intended to work with its European partners on a follow-on agreement which enshrines certain "triggers" that Iran cannot exceed related to ballistic missiles and inspections, said senior Trump administration officials on Friday while briefing reporters about Trump's decision.

Eliminating the "sunset clauses" that allow Iran to restart its uranium enrichment program after 2025 was also within Trump's concern, according to the officials.

Trump also wanted the U.S. Congress to amend a law on U.S. participation in the nuclear deal, so that Washington could reimpose all sanctions if Iran breaches certain "trigger points."

The U.S. president must sign a waiver suspending the U.S. sanctions on Iran every 120 days.

"So Trump now has issued an explicit May deadline to Congress and Europeans," said Mark Dubowitz, the executive director of the Foundation for Defense of Democracies, a Washington D.C.-based think tank.

"Is he bluffing? I don't think so," Dubowitz tweeted.

Also on Friday, the U.S. Department of Treasury imposed sanctions on 14 individuals and entities over Iran's alleged human rights abuses and ballistic missile program, including the head of Iran's judiciary and the cyber unit of the Islamic Revolutionary Guard Corps.

Despite the Iran nuclear deal, the United States has sanctioned around 100 individuals and entities involved in Iran's ballistic missile program and other activities which the United States saw as "illicit."

GLOOMY FUTURE FOR IRAN DEAL

Though Trump did not reimpose sanctions on Iran for now, his "ultimatum" still cast a dark cloud over the future of the 2015 nuclear deal, as both Iran and European countries have showed little interest in renegotiating the pact.

On Thursday, EU foreign policy chief Federica Mogherini, and foreign ministers of France, Germany, Britain, expressed their views to uphold the hardly-wrought deal.

Echoing Mogherini, French Foreign Minister Jean-Yves Le Drian said: "There is no particular reason to disengage in any way from this agreement as Iran has been respecting the provisions of the deal."

Hailing the deal as a "considerable diplomatic accomplishment," British Foreign Minister Boris Johnson said no one has so far come up with a better alternative.

"We know the EU and other powers want to keep the nuclear deal, almost no matter what," David Pollock, a senior fellow at the Washington Institute for Near East Policy, told Xinhua.

Meanwhile, experts say that quitting the deal is also against America's own strategic interests.

"His (Trump's) cabinet does not want him to cancel the nuclear deal because it could open up the region to nuclear proliferation," Darrell West, a senior fellow at the Washington-based think tank Brookings Institute, told Xinhua.

West believes that Iran could use that decision to restart its own nuclear program and that would encourage other countries in that region to do the same thing.

"If the United States reneges on its agreement, it will undermine global trust in America. Foreign leaders will doubt if they can trust U.S. agreements if the president renounces the agreement," West added.