Democratic presidential contender Hillary Clinton vowed Tuesday that Iran will never be able to acquire atomic weapons if she is elected to the White House.

Clinton's tough words came as critics in the US Congress, as well as skeptical US allies around the globe, criticized an agreement with Tehran as providing a glide path -- albeit a somewhat delayed one -- toward an eventual nuclear weapon.

"As president, I would use every tool in our arsenal to compel rigorous Iranian compliance," Clinton said in a statement.

"The message to Iran should be loud and clear: We will never allow you to acquire a nuclear weapon; not just during the term of this agreement -- never."

A former US secretary of state, Clinton said she is "still studying the details" of the plan, but gave it her qualified backing.

"Based on the briefings I received and a review of the documents, I support the agreement because it can help us prevent Iran from getting a nuclear weapon," the ex-first lady said.

"With vigorous enforcement, unyielding verification and swift consequences for any violations, this agreement can make the United States, Israel and our Arab partners safer."

The deal, hammered out between six world powers and Iran, was finalized in Vienna after marathon talks.

Clinton said, however, that inking the accord is just a first step, and that "effective enforcement" of the deal will be of paramount importance.

"In light of the international community's long history and experience with Iranian behavior, the highest priority must be given to effective enforcement of the agreement," she said.

"Signing is just the beginning. As president, I would use every tool in our arsenal to compel rigorous Iranian compliance."

Israel in particular, has been vocal about its displeasure over the Iran deal, which seeks to ensure that Tehran cannot create a nuclear bomb in return for lifting biting sanctions that have crippled the Islamic republic's economy.

Israeli Prime Minister Benjamin Netanyahu -- who has clashed publicly and frequently with US President Barack Obama over the content of the deal -- called it a "historic mistake" and signaled he remains ready to order military action against Iran.

Clinton was eager to acknowledge Israeli concerns, saying in her statement, that "even with a nuclear agreement, Iran poses a real challenge to the United States and our partners and a grave threat to our ally Israel."

Obama will hold a press conference on Wednesday to convince Americans, allies and skeptics about the merits of the deal.

Congress has 60 days to review the agreement reached between Tehran and Britain, China, France, Russia and the United States plus Germany (the so-called P5+1) to end a more than 13-year standoff.

Obama has vowed to veto any attempt to block it.