Former Secretary of State John Kerry slammed President Trump after he threatened to remove the U.S. from participating in the Iran nuclear agreement unless stricter conditions are implemented that hinder Iran's ability to advance its missile and nuclear capability.

"President Trump's decision today is dangerous," Kerry said in a statement Friday. "He's creating an international crisis. It endangers America's national security interests and those of our closest allies."

"I can't tell you why the President can't acknowledge what the [International Atomic Energy Agency], our allies, and the adults in his own cabinet all know to be true: Iran has lived up to its end of the nuclear agreement, and as long as they continue to do so, we and our allies are infinitely more secure than we would be without it," he added. "But whatever his reasons, the reality is that by destabilizing the agreement, the President weakens our hand, alienates us from our allies, empowers Iran hardliners, makes it harder to resolve North Korea, and risks moving us closer to military conflict."

Kerry, who served as the nation's top diplomat under former President Barack Obama, was an instrumental leader in the development of the Iran deal, struck in 2015, which aimed to freeze Iran's nuclear program in exchange for sanctions relief. He is not alone in rebuking Trump's maneuver, as some Democratic lawmakers have expressed concern that backing out of the deal could lead to war in the Middle East and the Korean Peninsula.

"If the Iran agreement falls, war will become much more likely – both in the Middle East and on the Korean Peninsula – and American lives will be put at risk," Sen. Chris Murphy, D-Conn., said Friday.

Additionally, Democrats, including some who opposed the nuclear deal, have expressed concern that withdrawing from the deal could escalate the tension that already exists with North Korea because it will eliminate the potential to create an agreement with North Korean leader Kim Jong Un.

"Our allies and adversaries alike will see this as a signal that the United States doesn't live up to our commitments, making the United States a source of uncertainty instead of a force for solving serious problems," New York Rep. Eliot Engel, the top Democrat on the House Foreign Affairs Committee, said Friday. "I have to ask: what major power will trust our word on potential North Korean nuclear negotiations, given how Trump is undermining the agreement with Iran?"

Trump announced Friday that he could not certify the Iran nuclear deal due to Iran's continued military aggression, support for terrorism, and difficulty verifying whether Iran is not covertly advancing nuclear weapons capability.

"Based on the factual record I have put forward, I am announcing today that we cannot and will not make this certification," Trump said.

Trump has not officially removed the U.S. from the deal, known as the Joint Comprehensive Plan of Action, and called on Congress and foreign allies to address the agreement's "many flaws."