A pro-ISIS twitter account has threatened attacks at London Heathrow, LAX and New York's JFK airports over the July 4 holiday weekend.

The account said that attacks would be carried out on planes 'flying from Heathrow [Airport] to the US' and warned that 'there will be a device placed in either Heathrow, LAX or JFK airports.'

The threat was revealed by SITE Intelligence Group - the world's leading non-governmental counterterrorism organization - on its website.

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Lengthy lines await holiday weekend travelers at New York City's JFK airport in the wake of heightened security fears following deadly attacks at Istanbul airport and Dhaka - which ISIS have claimed responsibility for

Security increases for the holiday weekend: A Transportation Security Administration employee checks passenger tickets as they get into the security line at JFK

Target: A pro-ISIS Twitter account has threatened to bomb planes flying out of Heathrow in London flying towards LAX and JFK in New York City

The account said that attacks would be carried out on planes 'flying from Heathrow [Airport] to the US' and warned that 'there will be a device placed in either Heathrow, LAX or JFK airports.'

The group is directed by founder Rita Katz, who has tracked and analyzed global terrorism and jihadi networks for nearly two decades.

She is well-recognized as one of the most knowledgeable and reliable experts in the field and has received special recognition from FBI Director Robert Mueller for her 'outstanding assistance to the FBI in connection with its investigative efforts.'

British Transport minister Lord Ahmad of Wimbledon called for the British public to be cautious.

He said: 'We all need to be vigilant to the global threat of terrorism - in the UK we keep all aspects of aviation security under constant review and work closely with our international partners to mitigate risks.

'We will continue to take all steps necessary to keep the public safe, but for security reasons we do not comment in detail on specific measures or operational matters.'

Heathrow Airport declined to comment on the apparent threat and referred inquiries to the Department for Transport.

This comes as authorities in the US brace themselves for a weekend of traffic chaos as it was revealed that up to 43 million people will be travelling across the country for Fourth of July weekend.

Huge firework displays will take place across the nation, as well as concerts and family fun days.

On Thursday, the FBI said there are no specific or credible security threats against the United States known to law enforcement heading into the Fourth of July weekend.

'However, law enforcement and members of the public must remain vigilant. ... The FBI asks members of the public to maintain awareness of their surroundings and to report any suspicious activity to law enforcement,' an FBI spokeswoman said in a statement.

An internal briefing document shared with government officials and called for the Department of Homeland Security to be on alert following recent attacks, such as the mass shooting in Orlando, Florida, on June 12, and calls from Islamic State supporters for attacks in the Western Hemisphere.

Nationwide alert: San Diego Harbor Police keep watch as travelers arrive on the departure level at Lindbergh Field airport in San Diego

Taking no chances: Members of the Armed Forces stand guard at Grand Central Terminal in New York City

Vigilance: Port Authority police officers stand guard near a departures entrance at John F. Kennedy International Airport

On Thursday, the FBI said there are no specific or credible security threats against the United States known to law enforcement heading into the Fourth of July weekend

On alert: A U.S. Customs and Border Protection officer patrols outside of the departures area at Miami International Airport

The absence of known threats does not ensure safety.

There were no threats known before the Orlando massacre, in which a gunman who pledged loyalty to Islamic State killed 49 people and wounded 53 more in the deadliest mass shooting in modern U.S. history.

The document said mass transit systems are particularly vulnerable to attack. It also said an attack over the U.S. Independence Day holiday would garner media attention that would further Islamic State's propaganda efforts.

There was no mention in the FBI's statement or in the document of the gun and bomb attack that killed 44 people at Istanbul's airport on Tuesday.

The threat was revealed by SITE Intelligence Group - the world's leading non-governmental counterterrorism organization - on their website (stock image of LA airport)

In the wake of the Istanbul attack experts have called for a worldwide rethink on airport security.

The demands reflect the increased likelihood of terror attacks throughout Europe, with seven countries across the continent considered 'high risk' by the British Foreign and Commonwealth Office.

Indeed, the June 28 attack in Turkey hit one day after the US State Department issued a travel warning to American citizens about the increased terror threat in the Turkey - and to avoid the south of the country altogether.

The current threat level in Turkey is currently classified as an emergency alert.