During an event in Winnipeg, Canada, Hillary Clinton said Congress should not seek to increase the level of sanctions on Iran "until we really know whether there's something that we can get out of them." (Reuters)

WINNIPEG, Canada - New congressional sanctions on Iran would give Iranian allies Russia and China an excuse to to back out of international negotiations and destroy chances for a nuclear deal, former secretary of state Hillary Rodham Clinton said Wednesday.

The likely Democratic presidential candidate praised President Obama's strategy of holding off on new penalties against Iran while seeking a deal to curb that nation's nuclear program. The United States and many other nations suspect Iran has used its nuclear research as cover for a secret weapons development program.

"If the U.S. Congress imposes sanctions before we even know the answers to the questions we are asking, I think it is highly likely that Russia and China" would walk out and end the United Nations Security Council-backed effort to curb the Iranian program, Clinton said.

The White House is trying to quash a bipartisan proposal to levy new economic restrictions on Iran, arguing that the talks, already in overtime, must run their course. In his State of the Union address Tuesday, Obama repeated a threat to veto those sanctions, but the White House is worried that the current debate will poison what have been mostly cordial negotiations.

Clinton was Obama's chief diplomat when preparations for the talks were laid, but has also backed harsh penalties against Iran in the past. She said she agrees with Obama that "no deal is better than a bad deal," but that a good deal is still possible.

Speaking at a forum sponsored in part by Canadian businesses, Clinton said additional sanctions would give "Iran and others an excuse not to continue negotiations" at a time when existing sanctions and falling oil prices appear to be helping U.S. bargaining power.

"That would be, in my view, a very serious strategic error," Clinton said. "Why would we want to be the catalyst for the collapse of negotiations before we really know whether there is something we can get out of them?"

House Speaker John A. Boehner on Wednesday invited Israel’s prime minister to speak next month before a joint meeting of Congress as part of the growing showdown. Israeli Prime Minister Benjamin Netanyahu quickly accepted the offer to make the address on Feb. 11. Israel opposes what Netanyahu sees as risky talks with its chief Mideast enemy.

Clinton's prepared remarks to a forum underwritten by Canadian bank CIBC focused largely on the global challenge of extremism and terrorism. The clash of ideas is "generational," but will be won by the example of democratic ideals and open societies, Clinton said.

She ducked a question about the proposed Keystone XL pipeline from Canada to the United States, telling CIBC President and CEO Victor Dodig that she is staying out of the State Department-led review process. In the past she has said it is inappropriate for her to comment because of her former role leading the department.

"You won't get me to talk about Keystone," Clinton said.

Clinton joked about her impending decision on whether to run for president a second time, but gave no hints about what she will do or when.