WASHINGTON -- President Barack Obama assailed critics of his Iran nuclear deal Wednesday as "selling a fantasy" to the American people, warning Congress that blocking the accord would damage the nation's credibility and increase the likelihood of more war in the Middle East.

Besides challenging opponents at home, Obama cast Israeli Prime Minister Benjamin Netanyahu as an isolated international opponent of the historic accord, saying, "I do not doubt his sincerity, but I believe he is wrong."

The agreement would require Iran to dismantle most of its nuclear program for at least a decade in exchange for billions of dollars in relief from international sanctions. But Netanyahu and some critics in the U.S. argue that it would not stop Iran from building a bomb.

The president's blunt remarks, in an hour-long address at American University, were part of an intense lobbying campaign by the White House ahead of Congress' vote next month to either approve or disapprove the international agreement. Opponents of the agreement have streamed to Capitol Hill, too, to make their case, and they have spent tens of millions of dollars on advertisements.

The stakes are high, Obama said, contending that it isn't just Iran's ability to build a bomb that is on the line but also "America's credibility as the anchor of the international system."

"The choice we face is ultimately between diplomacy and some form of war," Obama said. "Maybe not tomorrow, maybe not three months from now, but soon."

Obama's diplomatic overtures to Iran, a centerpiece of his foreign policy agenda, have put him at odds with Republicans and some Democrats, as well as with Netanyahu, who has campaigned vigorously against the deal.

Netanyahu and U.S. critics of the Iran deal say Obama is presenting a false choice between accepting the deal at hand and going to war to stop Iran from building a bomb.

Obama told Jewish leaders in a private meeting Tuesday that he understood their concerns about being cast as warmongers. But he made his case even more aggressively Wednesday by linking critics of the deal to those who pushed for the invasion of Iraq in 2003, a conflict now widely considered a mistake.

"I have repeatedly challenged anyone opposed to this deal to put forward a better, plausible alternative," he said. "I have yet to hear one. What I've heard instead are the same types of arguments that we heard in the run-up to the Iraq war."

Drawing on more distant history, Obama said the Iran deal was in line with America's long tradition of "strong, principled diplomacy" with adversaries, including the former Soviet Union. He spoke at the same university where John F. Kennedy called for Cold War diplomacy and nuclear disarmament, and he referred to Presidents Kennedy and Ronald Reagan a number of times.

The Iran accord was finalized last month after more than a year of tense negotiations between Iran, the U.S., Britain, France, Germany, China and Russia. The president argues that if Congress blocks the accord, the European Union and the United Nations will lift their sanctions anyway, collapsing the best leverage the international community has to stop Iran from building a bomb.

Opponents say the deal leaves too much of Iran's nuclear infrastructure in place and allows Tehran to rebuild its program too quickly. Critics also contend Iran will use an influx of funds now frozen under the sanctions to boost terrorist activity around the Middle East.

The White House is preparing for the likelihood that lawmakers will vote against the deal next month and is focusing its lobbying efforts on getting enough Democrats to sustain a presidential veto. Only one chamber of Congress is needed to sustain a veto and keep the deal in place.

Obama needs 146 Democrats in the House or 34 in the Senate to sustain a veto. The White House has said it is confident it can sustain a veto at least in the House.

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Associated Press writers Josh Lederman, Donna Cassata and Deb Riechmann contributed to this report.