Vice President Biden said Monday that President Obama is not "bluffing" about his willingness to use military force to prevent Iran from acquiring a nuclear weapon -- as Israeli Prime Minister Benjamin Netanyahu claimed Iran is inching closer to what he calls the "red line."
Both leaders spoke at the annual conference for the American Israel Public Affairs Committee, the powerful pro-Israel lobby. Netanyahu made clear he does not think Iran has yet crossed the "red line" -- which he defines as making 90 percent of the progress toward bomb-ready uranium.
But he warned that Iran is getting closer and beseeched the international community to prevent that outcome.
"We shall always defend the one and only Jewish state," Netanyahu said.
Biden told AIPAC that protecting Israel is in the United States' interest -- he said the U.S. still prefers a diplomatic option on Iran but that the window for that is closing.
Biden said efforts to delegitimize Israel as a Jewish state are the most dangerous changes he's seen as it relates to Israel's security. He said Israel's legitimacy is non-negotiable for the U.S.
"It is not a matter of debate. Don't raise it with us. Do not raise it with us," Biden said. "It is not negotiable."
Arguing the U.S. and Israel have a shared interest in preventing Iran from acquiring a nuclear weapon, which Israel views as an existential threat, Biden said the Obama administration would not back down from its pledge to intervene militarily should all other options fail.
"President Barack Obama is not bluffing," Biden said.
Biden also sought to clarify the Obama administration's policy toward its nuclear program -- which is to "prevent" a nuclear weapon, not "contain" it.
This comes after Obama's newly confirmed Defense Secretary Chuck Hagel, during his confirmation hearing, flubbed the issue and initially described a policy of containment. He later corrected himself, but throughout the process faced criticism from Republicans that he was not sufficiently tough on Iran or supportive of Israel.
The Associated Press contributed to this report.