US President Barack Obama will hold a press conference Wednesday as he tries to convince Americans, allies and skeptical lawmakers about the benefits of a nuclear deal with Iran.

Obama will answer questions in the East Room of the White House, spokesman Josh Earnest said Tuesday. The event is scheduled for 1:00 pm local time (1700 GMT).

With Congress set to vote on the deal and Republicans already clamoring against it, the White House is aggressively making its case.

Obama must garner the backing of a majority of Democrats in the Republican-controlled Congress to keep the deal alive.

Earnest said Obama had already been briefing some lawmakers on the deal.

The presumptive favorite to be the Democratic nominee, Hillary Clinton, was also contacted.

Behind the scenes, the White House has been briefing Congress, journalists, foreign governments and non-governmental groups about the talks since a framework agreement was reached in Switzerland in April.

But news of Tuesday's deal has sparked a fierce lobbying battle in Washington.

Experts have come out "for" and "against" as both sides try to sway public opinion.

Lobby groups have deployed multi-million-dollar budgets to make their case.

Obama's supporters fear a tight vote in Congress, even one in which the president prevails, could open the door for sustained attack on the deal.

Many Republican candidates to be president in 2016 have already vowed to repeal it.

Amid this barrage, the White House is expected to launch a communications campaign matching anything Obama's administration has done to date.

Cabinet members, senior officials and the president himself have already rolled out to sell the deal.

On Tuesday Obama spoke to leaders in Britain, Germany, France, the European Union, the United Arab Emirates, Saudi Arabia and Israel to make his case for the deal.

In the Gulf and in Israel, views about the deal ranged from anger to dismay.

Obama stressed however that his White house would still counter Iran's destabilizing activities in the region.

Speaking to the New York Times, the US president said the deal could only be judged a success based on whether Iran acquires a bomb.

"We are not measuring this deal by whether it is changing the regime inside of Iran," Obama told the newspaper.

"We're not measuring this deal by whether we are solving every problem that can be traced back to Iran, whether we are eliminating all their nefarious activities around the globe.

"We are measuring this deal -- and that was the original premise of this conversation, including by Prime Minister Netanyahu -- (on whether) Iran could not get a nuclear weapon."

Obama said he will be able to prove "by a wide margin," that the agreement was the best way to achieve that end.