Every US senator has signed a letter calling for greater federal help in tackling a new wave of bomb threats against Jewish community centres.

Police from New York to Florida and even in Canada, are scrambling to respond to a slew of threats that emerged overnight and resulted in lockdowns and evacuations. The Anti-Defamation League, a Jewish civil rights organisation, also said it received bomb threats at four of its locations.

“We’ve never seen such a period of concentrated threats against the Jewish community,” New York Mayor Bill de Blasio told a news conference. “The last few weeks are more troubling than anything I’ve seen in many, many years.”

Each of the US senators signed the letter calling for extra federal help (CNN)

US federal authorities have been investigating a surge of threats against Jewish organisations, including more than 100 hoax bomb threats in five separate waves in January and February in more than a dozen states, said Reuters.

The Jewish Community Centre (JCC) Association of North America confirmed the developments.

“JCC Association of North America confirms a developing situation in which several JCCs have received either emailed or phoned-in bomb threats overnight and this morning,” it said. “We will follow up with more information as it becomes available.”

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The Trump Administration denounced the newest round of threats “in the strongest terms”, White House spokesman Sean Spicer told a news briefing.

“As long as they do continue, we’ll continue to condemn them and look at ways in which we can stop them,” said Mr Spicer.

In addition to violent threats, some Jewish organisations received harassing phone calls. At the East Midwood Jewish Centre in Brooklyn, New York, police said, an anonymous caller threatened to spray the centre’s synagogue with pig’s blood.

Tuesday’s threats appeared unconnected to the majority of previous threats, according to the Secure Community Network, which provides security expertise to Jewish groups.

A letter signed by all 100 US senators was sent on Tuesday to top US law enforcement officials asking that they help Jewish groups enhance security.

“We are concerned that the number of incidents is accelerating and failure to address and deter these threats will place innocent people at risk and threaten the financial viability of JCCs,” the letter said.