By Steve Holland and Jonathan Landay
WASHINGTON (Reuters) - U.S. President Donald Trump is expected to strike a blow against the 2015 Iran nuclear agreement on Friday in defiance of other world powers, choosing not to certify that Tehran is complying with the deal in a major reversal of U.S. policy.
While Trump is unlikely to pull the United States out of the agreement, aimed at preventing Iran from developing a nuclear bomb, he is expected to give the U.S. Congress 60 days to decide whether to reimpose economic sanctions on Tehran that were lifted under the pact.
That would increase tension with Iran as well as put Washington at odds with other signatories of the accord such as include Britain, France, Germany, Russia, China and the European Union.
Trump is set to present a tough new strategy against Iran in a 12:45 p.m. EDT (1645 GMT) speech at the White House, the product of weeks of internal discussions between him and his national security team and which will also include a more aggressive approach to the growing Iranian influence in the Middle East.
"It is time for the entire world to join us in demanding that Iran's government end its pursuit of death and destruction," Trump said in a White House statement that flagged key elements of the strategy.
U.S. officials said Trump was expected to announce that he will not certify to Congress that Iran is complying with the accord, one he has called the "worst deal ever" as it was not, in his view, in the U.S. national interest.
Michael McCaul, chairman of the U.S. House of Representatives Homeland Security Committee, told Reuters he thinks Trump "is likely to not completely pull out of the deal, but decertify compliance."
If Washington quits the deal, that will be the end of it and global chaos could ensue, Iran's influential parliament speaker, Ali Larijani, was quoted by the Russian news agency TASS as saying during a visit to St Petersburg on Friday.
"FOOTPRINTS ON THE GROUND"
U.N. nuclear inspectors say Iran is in compliance with the accord, which limited the scope of Iran's nuclear program to help ensure it could not be put to developing bombs in exchange for a lifting of international sanctions on Tehran.
Trump says Tehran is in violation of the spirit of the agreement and has done nothing to rein in its ballistic missile program or its financial and military support for the Lebanese Shi'ite movement Hezbollah and other militant groups.
Trump found himself under immense pressure as he considered de-certifying the deal, a move that would ignore warnings from inside and outside his administration that to do so would risk undermining U.S. credibility abroad.
He had formally reaffirmed it twice before but aides said he was reluctant to do so a third time. The deal was negotiated under Trump's predecessor, former President Barack Obama.
White House Chief of Staff John Kelly said on Thursday the U.S. approach toward Iran is to work with allies in the Middle East to contain Tehran's activities.
"We have footprints on the ground, naval and Air Force is there to just demonstrate our resolve, our friendship, and try to deter anything that any country out there may do," Kelly told reporters.
European allies warn of a split with the United States over the nuclear agreement, in part because they benefit economically from a relaxation of sanctions.
The leaders of Britain and France have personally appealed to Trump to re-certify the nuclear accord for the sake of allied unity.
Germany's government pledged on Friday to work for continued unity if Trump de-certified the deal as Berlin remain convinced the agreement was an important tool to prevent Iran developing nuclear weapons.
Foreign Minister Sigmar Gabriel underlined German views in a telephone call with U.S. Secretary of State Rex Tillerson late on Thursday, his spokeswoman Maria Adebahr told reporters.
Russian President Vladimir Putin's spokesman, Dmitry Peskov, said that if the United States ditched the nuclear pact, "this will damage the atmosphere of predictability, security, stability and non-proliferation in the entire world".
REVOLUTIONARY GUARDS
McCaul said he expected Trump also to announce some kind of action against the Iranian Revolutionary Guard Corps (IGRC), the country's most powerful security entity. Trump is under a legal mandate to impose U.S. economic sanctions on the Revolutionary Guards as a whole by Oct. 31 or waive them.
U.S. sanctions could seriously hurt the IRGC as it controls large swaths of Iran's economy. The Guards' foreign paramilitary and espionage wing, the Quds Force, is under U.S. sanctions, as is the Quds Force commander, other officials and associated individuals and entities.
The deputy Quds commander, Brigadier-General Esmail Ghaani, was quoted by Iran' Tasnim news agency on Friday as saying Trump's threats would "damage" the United States.
"We are not a war-mongering country. But any military action against Iran will be regretted... We have buried many... like Trump and know how to fight against America," Ghaani said.
Israel, Iran's arch-adversary in the Middle East, welcomed Trump's anticipated announcement on Friday but voiced doubt that the tougher tack by Washington could turn around the Islamic Republic.
The International Atomic Energy Agency concluded that Iran secretly researched a nuclear warhead until 2009, which Tehran denies. Iran has always insisted its uranium enrichment activity is for civilian energy purposes, not for atomic bombs.
The threat of new U.S. action has prompted a public display of unity from rival factions among Iran's rulers.