U.S. Senate candidate Elizabeth Warren left the door open yesterday to military action against Iran in the face of that country’s growing nuclear threat — bolstering her national security credentials as she looks to challenge U.S. Sen. Scott Brown on one of his bread-and-butter campaign issues.

“Our number one responsibility is to protect Americans from terrorism, that’s our job, so being tough on terrorism is enormously important,” said Warren yesterday at a campaign stop in Gloucester.

“We should take nothing off the table, but the facts are still emerging,” the Senate candidate said when asked if she would support military action against Iran.

Her remarks come after two men, including a member of Quds Force, Iran’s special foreign actions unit, were charged in New York federal court Wednesday with conspiring to kill the Saudi ambassador to the United States on American soil. President Obama said yesterday Iranian officials “were aware of this plot.”

Warren, a Harvard Law professor and former Obama adviser, already touted her support of the military during a UMass-Lowell/Boston Herald debate, saying she encouraged her son to join the armed services. All three of her brothers served in the military.

Brown, who serves in the National Guard and has made homeland security one of his signature issues while in the Senate, said the United States needs to take action against Iran if facts prove that nation is behind the assassination plot.

“If in fact it’s true, then those folks need to be held accountable. Iran has for too long been spreading its tentacles across Afghanistan, and to move forward and try to do something (in the United States) is a bold move,” Brown told the Herald.

The Wrentham Republican co-sponsored a bill Wednesday to strip so-called “homegrown terrorists” of their citizenship. The legislation comes after an Ashland man was charged with plotting to bomb Washington, D.C., using large model planes.

Warren declined to discuss the bill, saying she hadn’t seen it.

But Alan Khazei, also seeking the Bay State Democratic nomination to run against Brown, called the legislation “more empty symbolism from Scott Brown.”

Brown dismissed the claim, saying “I know everyone is in gotcha campaign mode, but I’m trying to solve real problems.”