When America's top intelligence official said that Iran's regime is considering attacks on U.S. soil, he cited a single incident and qualified the assessment with a "probably."
But intelligence and law enforcement experts say the Jan. 31 warning by the director of national intelligence, James Clapper, was likely based on more than the evidence he cited.
"I would be surprised to learn a statement like that was not backed up by intelligence," said Mark Dubowitz, executive director of the Foundation for Defense of Democracies, a think tank.
The question of whether Iran will respond to international pressure with terror attacks on overseas targets is of particular concern to Jewish communities.
While there has been much speculation over how Iran would respond to an Israeli or American strike, experts are citing with concern a series of recent foiled plots, allegedly connected to Iran or its proxies, against Jewish and non-Jewish targets.
In his written, unclassified testimony submitted to the U.S. Senate's Select Committee on Intelligence, Clapper cited only the alleged plot revealed in October to assassinate Saudi ambassador Adel Al-Jubeir at the Cafe Milano, a popular Georgetown hangout for the powerful and influential. The attack allegedly had the backing of the Iranian Revolutionary Guard Corps.
"The 2011 plot to assassinate the Saudi ambassador to the United States shows that some Iranian officials -- probably including Supreme Leader Ali Khamenei -- have changed their calculus and are now more willing to conduct an attack in the United States in response to real or perceived U.S. actions that threaten the regime," Clapper wrote.
Matthew Levitt, a former deputy assistant secretary for intelligence and analysis at the U.S. Treasury under President George W. Bush, said Clapper's inclusion of Khamenei in his warning, even with the "probably" qualification, was no accident.
"People are careful to say what they mean, and nothing more," he said of the intelligence community. "As soon as I read that, I said, 'Uh-oh, that's not just a statement to say the threat to the ambassador was real," Khamenei was in there to say "it went to the top."
Sources close to law enforcement say there is no specific threat of an attack, although the FBI and the Department of Homeland Security in recent weeks have intensified their monitoring of possible threats.
ABC News cited an Israeli internal security document when it reported Feb. 3 that Jewish and Israeli institutions in the United States are on high alert over concerns that they will be targeted by Iran or its proxy. According to ABC, the head of security for the Israeli Consulate General for the Mid-Atlantic states in Philadelphia, wrote in a letter that the security threat has increased on "guarded sites" such as Israeli embassies and consulates, and "soft sites" such as synagogues, as well as Jewish schools, restaurants and Jewish community centers.
ABC reported that local and regional law enforcement and intelligence officials in U.S. and Canadian cities like New York, Los Angeles, Philadelphia and Toronto have increased security at Israeli and Jewish institutions, and that federal officials also have increased vigilance in looking for imminent attacks.
"In the past few weeks, there has been an escalation in threats against Israeli and Jewish targets around the world," ABC quoted a U.S. intelligence document as saying. It said that "many demonstrations against Israel are expected to be concentrated on Israeli embassies and consulates. Such demonstrations have occurred internationally as well as domestically. These demonstrations could potentially turn violent at local synagogues, restaurants, the Israeli Embassy and other Israeli sites."
The document said that "law enforcement should be vigilant when making periodic checks at all Jewish facilities."
An Israeli intelligence report warned that forged Israeli passports might be used by potential terrorists to leave the Middle East and enter the United States and Canada.
As the tensions over Iran's nuclear program mounted, Jewish security professionals noted the possible threat to Jewish institutions around the world.
A number of disrupted plots overseas in recent weeks have raised concerns, said Paul Goldenberg, national director of the Secure Community Network, an effort funded by the Jewish Federations of North America that works on strengthening security for Jewish institutions.
"The people that want to come after Israel overseas will look at Jewish targets in the host nations as well," he said. "They will look not just at embassies, but at synagogues and JCCs as secondary targets."
An example cited by Goldenberg of the conflation of Jewish and Israeli targets was the late January arrests in Azerbaijan of two citizens of that country in connection with an alleged plot to kill two rabbis and the Israeli ambassador in the capital city, Baku.
Three men reportedly were charged with weapons smuggling as part of the plot to kill the rabbis, who worked for a Chabad Jewish school in Baku, as well as the Israeli ambassador. Two of those charged are reported to be in custody; one is still at large.
Azerbaijan's national security ministry accused Iranian intelligence agents of arming and equipping the three men, the Israeli daily Ha'aretz reported. Ha'aretz suggested the plot was intended as retaliation for the assassinations of Iranian nuclear scientists. Israel's Counterterrorism Bureau has issued a travel warning for Azerbaijan.
Levitt, who is now a senior fellow at the Washington Institute for Near East Policy, said there was a period in which Iran was reluctant to strike out against targets overseas.
Iran was implicated in the 1994 bombing of the AMIA Jewish community center in Buenos Aires that killed 85 people and wounded hundreds. An Argentine prosecutor eventually accused five Iranians and the operational chief of the Lebanese Shi'ite milita Hezbollah, Imad Mughniyah, of involvement in the attack. Interpol issued warrants for their arrests in 2007.
Iran, which has always denied involvement in the AMIA attack, was stung by the diplomatic backlash in its wake, and it is widely believed to have ordered its proxies to confine operations to the Middle East.
The trigger that renewed the threat of attacks overseas was the assassination of Mughniyah by a car bomb in Syria in 2008. Hezbollah blames Israel's Mossad for the assassination, Levitt said.
"We will pick the time, the place, the punishment, the means and the method," said Hezbollah's Sheik Hassan Nasrallah.
Jewish communities in the United States and overseas have issued security alerts each year since then on the Feb. 12 anniversary of the killing.
Levitt said the intensification of Iran's isolation as the result of sanctions targeting its suspected nuclear weapons program and the heightened U.S. military posture have likely contributed to the intelligence community's sense that more attempts on overseas targets may be imminent.