US Republican Senator Jeff Flake has come out against the Iran nuclear agreement in a move that thwarted President Barack Obama’s attempts to build bipartisan support for it in Congress.

“While I have supported the negotiations that led to the JCPOA (Joint Comprehensive Plan of Action), from the beginning, I cannot vote in support of this deal,” Flake said in a statement.

The Arizona senator said the agreement reached between Iran and the P5+1 group of countries-- the United States, Britain, France, China, Russia and Germany – in Vienna last month, “does contain benefits” in terms of limiting Iran’s nuclear program.

“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,” he added.

The United States, Israel, and some of their allies accuse Iran of pursuing military objectives in its nuclear program.

In accordance with the Vienna agreement, Iran has been recognized by the United Nations as a nuclear power and will continue with its uranium enrichment program.

“While Congress has received assurances from the administration that it does not forfeit its ability to impose sanctions on Iran for behavior on the non-nuclear side, these assurances do not square with the text of the [Iran agreement],” Flake said.

Most Republicans oppose the nuclear agreement with Iran, but they need a two-thirds vote in both chambers of Congress to override a presidential veto.

The Republican-led Congress is reviewing the nuclear accord and is likely to vote on it in mid-September.

Obama needs the support of at least 34 senators to sustain a veto if Congress passes legislation to block the agreement.

Flake was considered the only potential GOP member able to give the Iran agreement some kind of bipartisan support.

Twenty Democrats in the Senate have so far announced that they support the agreement. A number of other Democrats, however, have since broken ranks with Obama on the issue.