By Patricia Zengerle

WASHINGTON (Reuters) - U.S. lawmakers this week will consider three Republican-backed measures targeting the Obama administration's nuclear agreement with Iran, which bitterly divides Washington a year after it was announced and could play a role in November's elections.

One bill would impose new sanctions on Iran over any sponsorship of terrorism or human rights violations. Another would bar the purchase from Iran of "heavy water," a non-radioactive byproduct from making nuclear weapons and nuclear energy. The third would block Iran's access to the U.S. financial system, including the use of the dollar.

Republican lawmakers, who control the House of Representatives and Senate and unanimously opposed the nuclear deal announced last July 14, have said the measures are necessary to send Iran a strong message that it will face consequences if it violates international agreements.

Many, joined by several Democrats, have been especially concerned by Iran's actions since the deal was officially implemented in January, including its test-firing of ballistic missiles in March.

"It makes sense to do all we can to check this very dangerous Iranian activity," Republican Representative Ed Royce, the chairman of the House Foreign Affairs Committee, told the Rules Committee, which sets up rules for debate of bills headed to the House floor.

Thanks in part to the nuclear agreement, Iran has begun to rejoin global politics and economics after more than three decades of isolation. Business and political leaders are visiting the country, which is also hosting trade conferences.

In his first report on the deal, United Nations Secretary-General Ban Ki-moon said Iran's ballistic missile launches "are not consistent with the constructive spirit" of the nuclear deal. He said it was up to the U.N. Security Council to decide if the launches violated the resolution backing the agreement.

However, he also said he was "encouraged by Iran's implementation of its nuclear commitments."

Republicans worry that President Barack Obama is so eager to preserve the pact as a legacy that his administration will give Tehran too much leeway before he leaves office in January.


Former Secretary of State Hillary Clinton, the presumptive Democratic presidential nominee, backs the nuclear deal. Republican candidate Donald Trump has promised to tear it up if he is elected on Nov. 8.

Most of Obama's fellow Democrats in Congress backed the agreement. They say the new legislation is intended to undermine or even derail it.

The White House issued a threat on Monday to veto all three bills, saying they would affect the continued viability of the nuclear agreement.

The deal "is critical to ensuring that Iran's nuclear program is and will remain exclusively peaceful, which is profoundly in the national security interest of the United States and the international community," it said in a statement.

The bills are not expected to win enough votes to advance in the Senate, even if they pass the House. And if they did pass the Senate, they would lack enough support to override a veto.

Backers of the Iran deal said Republicans were trying to appeal to voters just days before the convention where Trump is due to become the party's presidential nominee.

Polls show an overwhelming majority of Americans have an unfavorable view of Iran.

Dylan Williams, vice president for government affairs at J Street, a pro-Israel group that supported the nuclear deal, said such legislation plays into voters' frustration with what they see as a do-nothing Congress.

"This kind of grandstanding not only endangers our security by endangering the deal, it's exactly the type of politics that people are sick of," he said.

(Reporting by Patricia Zengerle; additional reporting by Michelle Nichols at the UNITED NATIONS; editing by David Gregorio)