Netanyahu, who faces a closely contested March 17 election in Israel, said he thinks the so-called P5+1 group of global powers is planning to ease international sanctions without the ironclad safeguards needed to deny Tehran a nuclear bomb.

As a result, he predicted Iran would be able to finance more terrorism in the region and the world.

The U.S. administration says that is just not true, and warned that Netanyahu's speech could unravel the negotiations if he mobilizes U.S. lawmakers in the Republican-held Congress against it.

Democratic Senator Dick Durbin said earlier Tuesday, "We [Democrats and Republicans] are in common purpose: to stop the development of a nuclear Iran. What troubles me greatly are the criticisms I have heard on this floor about the Obama administration and this issue. ... It was President Obama who really brought together the sanctions regime that is working to bring Iran to the negotiating table.”

The deal, as it now stands, would give Tehran some limited ability to enrich uranium – but Israel wants Iran stripped of its nuclear projects all together to ensure it can't pursue a bomb.

Iran's Foreign Minister Mohammad Javad Zarif said Tuesday that Netanyahu is trying to affect negotiations over Iran's nuclear program with his upcoming address to both chambers of the U.S. Congress.

"He's trying to, and I don't think trying to create tension and conflict helps anyone," Zarif said to cnn outside talks in Switzerland with U.S. Secretary of State John Kerry.