WASHINGTON - US President Barack Obama pledged Tuesday to test the sincerity of signs that new Iranian President Hassan Rowhani may be ready for a newly productive nuclear dialogue with the West.

Days after revealing he and Rowhani had swapped letters, Obama however said that Iran would have to demonstrate its own seriousness by agreeing not to “weaponize nuclear power.”

“There is an opportunity here for diplomacy,” Obama said in an interview with the Spanish language television network Telemundo. “I hope the Iranians take advantage of it. There are indications that Rowhani, the new president, is somebody who is looking to open dialogue with the West and with the United States — in a way that we haven’t seen in the past.

“And so we should test it,” Obama said.

Hopes for a new round of nuclear talks between Iran and world powers expected to resume soon were boosted earlier Tuesday by cryptic remarks by Iran’s Supreme Leader Ayatollah Ali Khamenei.

Khamenei, who bears ultimate responsibility for the nuclear issue, said that sometimes flexibility was necessary in diplomacy. On September 11, Rowhani said he had the tacit support of Khamenei for “flexibility” in nuclear talks.

Obama called on Congress to act on his stalled gun reform measures, bemoaning its failure to make meaningful reforms despite a “ritual” of shooting massacres.

He called on Congress to tighten gun laws but lawmakers admitted there is insufficient support for new legislation.

A day after a gunman shot dead 12 people at a US Navy facility a few miles from the White House, Obama said the “overwhelming majority” of Americans agreed with him on the need for common-sense firearms reform. “I do get concerned that this becomes a ritual that we go through every three, four months, where we have these horrific mass shootings,” Obama said in an interview with the Telemundo Spanish-language television network. “Everybody expresses understandable horror. We all embrace the families... and yet we’re not willing to take some basic actions.”

Meanwhile, the Pentagon was reviewing security at US bases worldwide Wednesday, after a defense contractor gunned down 12 people in Washington.

, as investigators worked to uncover the shooter’s motive.

US military officials, who announced the security review on Tuesday, were struggling to answer how and why 34-year-old Aaron Alexis — a former sailor with a history of disciplinary problems and brushes with the law — had been granted a security clearance.

Alexis opened fire Monday at the tightly guarded Washington Navy Yard, where he had a valid entry pass, according to the FBI. He eventually died in a shoot-out with police at the giant compound.

With lawmakers questioning the vetting of contractors, Defense Secretary Chuck Hagel “intends to order a review of physical security and access at all DoD (Department of Defense) installations worldwide,” a senior Pentagon official said.

The White House said President Barack Obama also ordered a review into security standards for contractors at federal agencies.

Monday’s mass shooting — which sparked a fresh call from Obama for Congress to act on gun law reform — left federal authorities acknowledging that their probe had much to uncover.

“As we have moved from a crisis stage to the investigation stage of this case, our focus and efforts are going to be on the questions we all have,” said US federal prosecutor Ronald Machen.

Obama has introduced a sheaf of measures including a plan for enhanced background checks on gun buyers and a ban on assault-style rifles as America reeled after 20 children and six adults were killed in a school rampage in Newtown, Connecticut last December.

Yet the package foundered in Congress, partly due to a fierce lobbying campaign by pro-gun groups and opposition from some of his fellow Democrats from conservative states, leaving Obama to introduce a smaller set of measures using his executive powers.

“Ultimately, this is something that Congress is going to have to act on,” he said in the interview. “I’ve taken steps that are within my control. The next phase now is for Congress to go ahead and move.”

Monday’s killings were greeted with a chorus of revulsion across the political spectrum, but as the previous gun-reform fight showed, it will take more than White House appeals for action to sway lawmakers.

Senate Majority Leader Harry Reid said he wanted to revive the debate sooner rather than later.

“But we’ve got to have the votes first. We don’t have the votes,” Reid said after meeting with fellow Democrats.

“I hope we get them but we don’t have them now.”

The blunt assessment by the man who schedules Senate floor debate speaks volumes about the uphill battle facing gun control advocates.

Several Democrats, including Senator Richard Blumenthal of Connecticut, said they hoped to reintroduce legislation on background checks and ensuring that the mentally ill would not have access to firearms.

“I think there is a potential opening for a new consensus and new momentum and impetus for gun violence prevention,” Blumenthal told AFP, but he acknowledged it would be a hard sell to Republicans, most of whom voted against expanding background checks in April.

That bill failed by five votes in the 100-seat Senate (Reid changed his vote to “no” so he could bring up the legislation again), and it would have been an even tougher political lift in the Republican-controlled House.

But Senator Chris Murphy said Americans won’t let lawmakers “ignore this continuing slaughter,” noting that more than 8,000 people have died in US gun violence in the nine months since Newtown.”

“People are just not going to accept that Congress continues to sit on its hands while these mass shootings happen,” he said.

Republican Senator Bob Corker did not foresee action on guns this year.

“I bet that doesn’t happen,” he told AFP. “Nobody is talking to me about (gun reform).”

Asked if he has sensed any shift in gun-control support after Monday’s tragedy, Senator Tom Carper said “I don’t think so.”

Carper, a Democrat who chairs the Homeland Security Committee, said he may soon hold hearings on security shortcomings that may have led to a mentally unstable contractor gaining legitimate access to a military base.

The suspect in Monday’s shooting, 34-year-old Aaron Alexis, was working on a Navy contract through computer giant Hewlett-Packard, but reports show he had prior run-ins with police.

“Whoever did the background check, were they aware of the earlier arrests, the charges?” Carper asked.

“I’m not sure that they were. So we’re going to drill down on this.”

Lawmakers including Senator John McCain, one of a handful of Republicans who voted for the background bill this year, said mental health could emerge as a focal point of legislation.

Most states mandate that people diagnosed as mentally ill be barred from purchasing a firearm, but critics argue that such laws are not fully enforced.

The White House meanwhile ordered a review into security standards for contractors at federal agencies following Monday’s shootings.

The review will be conducted by the White House Office of Management and Budget and will run at the same time as a separate probe into national security clearances launched in the wake of revelations by fugitive leaker Edward Snowden.