Secretary of State John Kerry on Tuesday defended the nuclear deal with Iran and said U.S. negotiators had driven a “hard bargain” to force concessions from Tehran.

“I want you to know these were not easy negotiations. We drove a very hard bargain to achieve what we needed to in terms of our verification and certainty about where they're going,” said Kerry in a video message.

“And we drove a hard bargain because we have one unwavering purpose in our goal. President Obama has been absolutely clear that Iran cannot and will not acquire a nuclear weapon,” he added.

The P5+1 group of key powers — including the U.S., United Kingdom, France, Germany, China and Russia — on Saturday reached an agreement with Iran that would see Tehran freeze some aspects of its nuclear program in exchange for limited sanctions relief. The deal sets the stage for further talks at a more comprehensive agreement on Iran’s nuclear ambitions.

Tehran insists its program is for peaceful energy purposes, but the international community fears it is building a bomb.

The administration though faces a hard sell with lawmakers and key U.S. allies, most notably Israel, skeptical that the deal will stop Iran from developing nuclear weapons.

The White House has urged lawmakers to give diplomacy more time and hopes to avert efforts by a bipartisan Senate group to pass new additional sanctions on Iran, which the administration fears could unravel the deal.

Kerry touted the diplomatic accord as the “first in almost a decade to put any kind of meaningful limits on Iran's nuclear program.”

“We're not just slowing down its progress; we're actually halting it and even rolling it back in some key areas,” he added.

The secretary of State said the sanctions relief given to Iran is “limited and reversible.”

“We all know that if the agreement falls apart, Iran is going to quickly face even tougher sanctions,” said Kerry.

Kerry said that he would also “immediately” begin work on a “final, comprehensive agreement” to address Iran’s nuclear program.

“We're going to get this done, I hope, but we're not cocky about it. We're not overconfident,” said Kerry. “It's going to take a lot of work, and in the end, it's really up to Iran to make the choice, to prove that its program is indeed peaceful.”