The remarks came at a joint news conference at the White House dominated by a host of global threats, including recent terrorist attacks in France, which have rattled Europe.

The two leaders pledged deeper cooperation on countering terrorism and on cybersecurity, with Obama seemingly open to Cameron’s call to step up pressure on technology companies such as Google and Facebook to better cooperate with governments as investigators look to disrupt terrorists.

Obama said disclosures by former government contractor Edward Snowden had ramped up anxiety about government interference, but he added, “We’re still going to have to find ways to make sure that if an al Qaida affiliate is operating in Great Britain or in the United States, that we can try to prevent real tragedy. And I think the companies want to see that as well.”

Cameron said he wasn’t looking for a new policy but that as technology developed “we should try to avoid the safe havens that could otherwise be created for terrorists to talk to each other.”

Obama said the U.S. was talking with its allies and technology companies in order to balance privacy with public safety.

“I’m actually confident that we can balance these imperatives, and we shouldn’t feel as if because we’ve just seen such a horrific attack in Paris that suddenly everything should be down by the wayside,” he said.

The two were in complete agreement on Iran, with Obama saying he’d told Senate Democrats on Thursday at a retreat in Baltimore that he’d veto legislation that seeks to impose more sanctions on Iran. He said the proposal could undermine the international coalition that’s pressing for a diplomatic resolution.

“My main message to Congress at this point is just ‘Hold your fire,’ ” Obama said. Cameron said he’d talked with several U.S. senators Friday to tell them that his government thought more sanctions wouldn’t help and might “fracture” the international effort.

A bipartisan group in the Senate argues that Iran agreed to negotiate only because of tough sanctions and more are needed to push Tehran to close the deal. Sens. Robert Menendez, D-N.J., and Mark Kirk, R-Ill., are readying legislation that would impose new sanctions in July if no deal has been reached.

“I do not believe in negotiating out of weakness. I believe in negotiating out of strength,” Menendez said in New Jersey after Obama’s remarks.

Menendez, who maintained he has a “fundamental difference” with the president, called the Iranians “masters of delay” and said it was “counterintuitive” that Iran would walk away from the table because of sanctions that wouldn’t be imposed if it struck a deal.

Obama pegged the chance of reaching a deal with Iran at “probably less than 50-50,” but said the interim deal that brought Iran to the negotiating table included a stipulation that the U.S. wouldn’t initiate new sanctions.

With new sanctions, he said, Iranian negotiators would be able to argue “the United States was operating in bad faith and blew up the deal. And there would be some sympathy to that view around the world.”

Obama pledged that if they didn’t reach a deal in a few months, “I will be the first one to come to Congress and say we need to tighten the screws.”

Obama and Cameron pledged support for France in the wake of the deadly terrorist attacks last week and spoke of maintaining vigilance against the threat posed by Islamic extremists. Cameron decried a “poisonous, fanatical death cult of a narrative that is perverting the religion of Islam.”

Obama said the U.S. had an advantage over Europe in combating violent extremists because of the U.S. tradition of assimilating new immigrants.

“Our Muslim populations, they feel themselves to be Americans,” he said, adding, “That is part of our tradition that is probably our greatest strength.”

He noted there were parts of Europe where “that’s not the case” and said it was crucial for the continent “not to simply respond with a hammer and law enforcement and military,” but to provide immigrants with a sense of identity and opportunity.

Obama declined to answer one question asked of him: his reaction to the news that Mitt Romney, his Republican challenger in the 2012 election, is considering another stab at the presidency.

“I have no comment,” Obama said, a smile flickering across his fac