The former White House official who resigned this week as head of a key US group lobbying against the Iran nuclear deal, warned the partisan row was hurting America's national interest.

Gary Samore, who stepped down as president of United Against Nuclear Iran because he supports the agreement, said a political battle between Congress and the White House had crowded out the "pragmatic center."

"This looks like it will be a straight-out political battle between Republicans and some Democrats against the White House and that's very unfortunate," Samore told AFP.

His resignation Monday thrust him into the center of the fierce battle over the Iran deal, one fueled by multi-million-dollar lobbying budgets and the 2016 presidential election campaign.

Samore, a non-proliferation expert, advised Barack Obama during his first presidential term and received wide media attention this week as former White House colleagues hailed his decision as a victory for the "yes" camp.

United Against Nuclear Iran immediately announced he would be replaced by anti-deal former senator Joe Lieberman and unveiled a multi-million dollar campaign to highlight "key deficiencies and weaknesses" in the agreement.

The Republican-controlled Congress is expected in September to vote against the deal, but is unlikely to have enough support to overturn Obama's veto.

"I don't know that this agreement is really going to survive 15 years, in fact my guess is that it probably won't," Samore said.

"But if the agreement collapses I have confidence in our ability to mobilize support for pressure against Iran or use military force if necessary."

"It would be much better if the White House and Congress could come to an agreement on a resolution of support, with conditions that would strengthen the elements of the deal," he added

Samore insisted Congress could have strengthened Obama's hand vis-a-vis Tehran by reinforcing the agreement with "conditions relating to the use of force if necessary, or responding to Iran's regional policy, or keeping Congress adequately involved in implementation."

"That would be, from a national interest standpoint, the best outcome," he said. "Unfortunately I think the politics preclude that from happening."

After the knock-down-drag-out Washington fight ahead in the next month, "I don't know how much political will be left for coming up with a compromise," he added.

- 'No basis to compromise' -

While the White House has been frustrated by Republicans' summary rejection of the deal -- in some instances before it was finalized. Obama has also been criticized for playing politics.

Critics roundly reject his suggestion that the only alternative to the deal is war.

The White House has "decided that there is no basis to compromise with the Republicans who are going to oppose this agreement no matter what," said Samore.

"They have decided that the only strategy that is going to succeed is to appeal to enough Democrats on the left to block a congressional override of the president's veto."

"The most effective political strategy is to make this an anti-war vote."

Samore explained his thinking after reading over the deal.

"I really do think there are solid grounds for reasonable people to come to different conclusions on this agreement," he said describing his decision.

"I think the strength of the agreement is that it limits Iran's ability to produce fissile material at its declared facilities for 15 years at least and establishes a versification and enforcement mechanism that will improve our ability to catch them cheating."

"On the negative side, the agreement allows Iran to retain a larger enrichment program than I am comfortable with and most of the critical limits expire in 15 years."

"But when you look at those pros and cons against the available alternatives, my conclusion is that this agreement is the most effective way to prevent Iran from producing nuclear weapons, at least for the time being."