[UPDATED] The US government has directed the Transportation Security Administration (TSA) to implement increased security measures for certain airports with direct flights to the US.

In a statement, Department of Homeland Security Secretary Jeh Johnson said the move was part of its continuous assessments of the global threat environment and reevaluations of measures necessary to ensure aviation security.

The airports affected were not named, but London Heathrow is reported to be among them. Airports were typically making no comment, but a number of European major hubs said it was business as usual and passengers were not seeing any disruptions.

“We are sharing recent and relevant information with our foreign allies and are consulting the aviation industry. These communications are an important part of our commitment to providing our security partners with situational awareness about the current environment and protecting the traveling public,” Johnson said.

“Aviation security includes a number of measures, both seen and unseen, informed by an evolving environment. As always, we will continue to adjust security measures to promote aviation security without unnecessary disruptions to the traveling public,” he added.

North American airline association Airlines for America (A4A) said it supports efforts to employ a targeted, risk-based security strategy, in conjunction with the multilayered approach already in place. “Our members work cooperatively with DHS on requirements it deems appropriate,” A4A said.