U.S. President Barack Obama believes Bashar Assad's backers in Moscow and Tehran may see the writing is on the wall for the Syrian regime, offering rare hope for a resolution to a bloody civil war.

Speaking to columnists in the White House on Wednesday to sell his nuclear deal with Iran, Obama also offered a glimmer of optimism about the dire situation in Syria.

Democratic Senator Chuck Schumer, the most influential Jewish voice in the U.S. Congress, announced Thursday he will oppose the Iran nuclear deal, a blow to President Barack Obama.

"Advocates on both sides have strong cases for their point of view that cannot simply be dismissed," Schumer, the number three Democrat in the Senate, said in a statement.

Iran's Foreign Minister Mohammad Javad Zarif is scheduled to visit Beirut next week to brief Lebanese officials on the nuclear deal signed between major powers and Tehran.

Zarif will make the visit on August 12. He is expected to meet with top officials and political figures who are allied with Iran.

President Barack Obama launched a blistering denunciation of opposition to his Iran nuclear deal Wednesday, arguing that none of the criticism stands up to scrutiny and warning that if Congress blocks the accord it will put the U.S. on the path to another Middle East war.

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

In 1963 U.S. President John F. Kennedy traveled the short distance from the White House to American University to muster support for diplomatic engagement with nuclear foe the Soviet Union.

On Wednesday, at the same spot, President Barack Obama will echo Kennedy's entreaty, arguing for a nuclear deal with Iran -- a country described by his predecessor as part of an "axis of evil."

President Barack Obama has warned that any possible rejection by the Congress of the Iran nuclear deal, would force the U.S. to attack Iran, a move that could lead to a Hizbulalh retaliation against Israel.

"It would be destructive both to the U.S. and to Israel," Obama told Jewish leaders on Tuesday, according to Israeli media reports.

U.S. President Barack Obama has extended the national emergency with respect to Lebanon that was declared in Executive Order 13441 of August 1, 2007.

He said in a statement released by the White House on Wednesday that “the national emergency is to continue in effect beyond August 1, 2015.”

U.S. Secretary of Defense Ashton Carter has sought to reassure worried lawmakers on the nuclear deal with Iran and stressed that the Islamic Republic and its proxies, including Hizbullah, continue to be a threat.

Iran and its proxies still present security challenges, Carter said on Wednesday at a committee hearing as part of the White House's aggressive campaign to convince Congress to back the Iranian nuclear deal, which calls on Iran to curb its nuclear program in exchange for billions of dollars in sanctions relief.

The Senate on Wednesday confirmed President Barack Obama's pick to be the next chairman of the Joint Chiefs of Staff.

Marine Gen. Joseph Dunford Jr., who is currently commandant of the Marine Corps, is expected to take over Oct. 1 for Gen. Martin E. Dempsey, who will retire after a 41-year Army career.

President Barack Obama said Tuesday that the United States stood with Africa to defeat terrorism and end conflict, warning that the continent's progress will "depend on security and peace".

"As Africa stands against terror and conflict, I want you to know the United States stands with you," Obama said in a speech to the African Union, highlighting threats ranging from Somalia's Shebab, Boko Haram in Nigeria, insurgents in Mali and Tunisia, and the Uganda-led Lord's Resistance Army rebels in central Africa.