Sen. Robert Menendez (D-NJ).
Washington CNN  — 

A heated exchanged between President Barack Obama and Sen. Robert Menendez (D-New Jersey) broke out Thursday over whether the U.S. should impose new sanctions on Iran amid ongoing negotiations over the country’s nuclear program, according to two senators who were in the room.

Menendez, the leading Democrat pushing for additional sanctions against Iran, forcefully pressed Obama on the need for additional sanctions during a meeting in which Obama urged Menendez and other senators to drop their efforts to pass sanctions legislation. Additional sanctions, Obama argued, could torpedo ongoing negotiations over Iran’s nuclear program.

The unusually sharp exchange, between a senior senator and a president from his own party, occurred during a Senate Democratic retreat at a hotel in Baltimore. A senior administration official also confirmed details of the exchange, which was first reported by the New York Times.

Obama said that as a former senator himself, he understood how outside forces – like special interests and donors – can influence senators to act, one of the senators recounted.

That’s when Menendez stood up to challenge the President, telling Obama he took “personal offense” to his assertions, the New York Times reported, arguing that he has worked to curb Iran’s nuclear ambitions for many years and was not motivated by political considerations.

“It was not confrontational. It was just a good lively exchange,” Sen. Tom Udall, D-New Mexico said. “We know there are some differences there. But they showed tremendous respect for each other.”

“I wouldn’t say he confronted the President,” said Sen. Bernie Sanders, an independent from Vermont who caucuses with the Democrats. “He has a different point of view than the President and Bob is a very smart guy. I don’t agree with him but he is entitled to his opinion.”

The senior administration official also described the exchange as respectful.

Obama said that he would support new sanctions if negotiations fail, but doing so while negotiations are ongoing would not only threaten the talks, but could shift the blame onto the U.S., and not Iran, if negotiations fail, the official said.

Obama asserted during a press conference Friday that he would veto a new sanctions bill, urging Congress to “hold your fire.”

“I will veto a bill that comes to my desk and I will make the argument to the American people as to why I’m doing so,” Obama said. “I respectfully ask them to hold off a few months to see if we have the possibility of solving a big problem without resorting possibly to war.”

Menendez would not comment on his exchange with the President because he doesn’t “violate my private conversations.”

“Having said that, on the issue, I have respect for the President but no one has followed this issue more in Congress that I have,” Menendez said at an event in New Jersey on Friday afternoon.

Menendez went on to express his frustration with a negotiation process that has been ongoing since late 2013, and again pushed for his bill, the latest version of which would not impose sanctions on Iran until July.

“I do not believe in negotiating out of weakness, I believe in negotiating out of strength. I think weakness invites provocation, I think strength avoids it. So it is counterintuitive to understand that somehow Iran will walk away because of some sanctions that would never take place if they strike a deal and or which the President has waiver authority,” Menendez said.

New Congress, new nuclear showdown over Iran

A sanctions bill sponsored by Menendez and Republican Sen. Mark Kirk of Illinois (known as Kirk-Menendez) failed to muster the 60 votes necessary to clear a filibuster last year after Obama threated to veto the legislation.

A new 54-member majority in the Senate has given Republicans and the dozen Democrats who staunchly support additional sanctions new drive to pass legislation this year – just as talks between the U.S., other world powers and Iran resumed this week.

Menendez and his Republican colleague should be able to easily rally the votes to clear a filibuster, but reaching the 67-vote threshold to override a presidential veto is another matter. Several Democratic supporter’s of last year’s bill were ousted in the midterms, and four others backtracked their support after the bill failed.

That is pushing Kirk and Menendez to rework the bill as they look to attract broader support, though Kirk told CNN last week that he is pushing to keep the bill largely intact.

Last year’s bill would have imposed stricter conditions on Iran to avoid additional sanctions, likely imposing sanctions before negotiations came to a term and prompting Iranian assertions that the bill’s passage would prompt them to ditch the negotiating table.

The Senate Banking Committee is holding a hearing Tuesday to discuss additional sanctions against Iran on Tuesday.

Asked if the President’s comments persuaded Menendez to drop new legislation, Udall was doubtful.

“We’ve had this discussion for months and months,” Udall said. “Since we’ve had so many discussions about it I’m not sure any one ten minute discussion about it is going to turn us one way or another.”

CNN’s Jim Acosta contributed to this report.