WASHINGTON: President Barack Obama launched an aggressive and detailed defense of a landmark Iranian nuclear accord, rejecting the idea that it leaves Tehran on the brink of a bomb and arguing the only alternative to the diplomatic deal is war.

The president vigorously challenged his critics during a lengthy White House news conference, a day after Iran, the US and five other world powers finalized a historic, years-long agreement to curb Tehran’s nuclear program in exchange for billions of dollars in sanctions relief. Opposition to the deal has been fierce, both in Washington and Israel.

“Either the issue of Iran obtaining a nuclear weapon is resolved diplomatically through a negotiation or it’s resolved through force, through war,” Obama said. “Those are the options.”

In Congress, resistance comes not only from Republicans, but also Obama’s own Democratic Party. Vice President Joe Biden spent the morning on Capitol Hill meeting privately with House Democrats, and planned to return Thursday to make a similar pitch to Democrats on the Senate Foreign Relations Committee.

The president said he welcomed a “robust” debate with Congress, but showed little patience for what he cast as politically motivated opposition. Lawmakers can’t block the nuclear deal, but they can try to undermine it by insisting US sanctions stay in place.

An hour into the East Room news conference, Obama asked if reporters had other questions about Iran — a highly unusual inquiry from a president who is rarely so freewheeling in his exchanges with the press. He pulled a piece of paper out of his pocket, saying he had “made notes” about the main criticisms of the deal and wanted to ensure each had been addressed.

Obama said the deal should be judged solely on whether it stops Iran from obtaining a nuclear weapon. As to whether the agreement might change Iran’s other behavior, he said, “We’re not betting on it.”

The president also sharply rebuffed a suggestion that he was content to let American detainees languish in Iran while he celebrated a deal. “That’s nonsense,” he said, adding that Iran would have taken advantage of any US effort to link the nuclear accord to the release of US citizens. Showing a command of technical nuclear issues, Obama spent much of the news conference trying to knock down criticisms of the deal point by point.

To those who argue sanctions relief will leave Iran flush with cash to fund terrorism, Obama said Tehran is already backing Hezbollah and other groups on the cheap. He noted that the Iranian government is under pressure from citizens to use any influx of international funds to improve the country’s struggling economy.

Obama insisted sanctions on Iran could be “snapped back” in place if Iran cheats on the deal, even if Russia and China object. He defended the 24-day window Iran would have before international inspectors gain access to suspicious sites, saying nuclear material “leaves a trace” and suggesting the US has other means of monitoring facilities.