U.S. Republican Senator Jeff Flake speaks to reporters as U.S. Democrat Senator Tom Udall listens during a news conference in Havana November 11, 2014. REUTERS/Enrique De La Osa

By Will Dunham

WASHINGTON (Reuters) - U.S. Senator Jeff Flake announced his opposition on Saturday to the nuclear deal with Iran despite White House lobbying to try to convince the Arizona Republican to break from others in his party and back the accord when U.S. lawmakers vote on it.

The agreement that Iran reached with the United States and other world powers on July 14 "does contain benefits in terms of limiting Iran's ability to produce sufficient fissile material for a nuclear weapon for a period of time, particularly at its known nuclear facilities," Flake said in a statement.

"But these benefits are outweighed by severe limitations the (agreement) places on Congress and future administrations in responding to Iran's non-nuclear behavior in the region," Flake added.

The White House had held out some hope that Flake, a Senate Foreign Relations Committee member, would buck his party and possibly bring some other Republicans with him in support of the agreement.

Flake was the only Republican lawmaker who traveled with President Barack Obama to Africa in July. White House officials lobbied him during that trip to support the deal. Flake had backed Obama's moves on another important foreign policy initiative, establishing warmer relations with Cuba.

White House officials declined comment on Flake's decision but noted seven Democrats had come out in favor of the deal in the past week.

When Congress returns to work on Sept. 8, debate will begin on a Republican-sponsored "resolution of disapproval" against the deal. That resolution is expected to pass. Obama is poised to veto such a measure, and would need 34 votes in the 100-seat Senate to block the override of that veto and preserve the Iran agreement.

The agreement would give Iran some relief from economic sanctions in return for strict limits on a nuclear program the West has suspected was aimed at creating nuclear weapons.

Flake backed the negotiations that produced the accord, but said, "I cannot vote in support of this deal." Flake said while Obama's administration has assured Congress it does not forfeit its ability to impose sanctions on Iran "for behavior on the non-nuclear side," those assurances do not square with the agreement's text.

"Hoping that Iran's nuclear ambitions might change after a 15-year sabbatical might be a bet worth making. Believing that Iran’s regional behavior will change tomorrow - while giving up tools to deter or modify such behavior - is not," Flake said.

(Reporting by Will Dunham and Jeff Mason; Editing by Peter Cooney, Bernard Orr)