Islamists claiming allegiance to Islamic State have issued a threat against Heathrow, LAX and JFK airports, warning that one of them would be targeted over the July 4th weekend. A transport minister has said that government is taking “all steps necessary to keep the public safe,” but advised continual vigilance by travellers. The threat, made by a “pro-Islamic State Twitter account,” was picked up by non-governmental counter-terrorism organisation SITE Intelligence Group on Friday, who issued an alert, the Telegraph has reported. The alert advised that the account had issued threats against planes “flying from Heathrow to the US” during the 4 July US Independence Day holiday weekend, and warned “there will be a device placed in either Heathrow, LAX [Los Angeles] or JFK [New York] airports”. Transport minister Lord Ahmed of Wimbledon has urged the public to be cautious, saying: “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