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

“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 during a White House news conference. “Those are the options.”

The president spoke one day after Iran, the U.S. and five other world powers finalized a historic, yearslong 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. Sunni Arab rivals of Shiite Iran also express concerns.

Israeli Prime Minister Benjamin Netanyahu, perhaps the fiercest critic of Obama’s overtures to Iran, showed no sign he could be persuaded to even tolerate the agreement. In remarks to Israel’s parliament, Netanyahu said he was not bound by the terms of the deal and could still take military action against Iran.

“We will reserve our right to defend ourselves against all of our enemies,” said Netanyahu, who sees Iran’s suspected pursuit of a nuclear weapon as a threat to Israel’s existence.

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 today 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 U.S. sanctions stay in place.

In Tehran, Iranians took to the streets to celebrate the accord, and even Iran’s hard-liners offered only mild criticism — a far cry from the outspoken opposition the White House had feared.