London Heathrow airport has issued updated security advice, warning travellers headed for the US any electronic devices must be charged.

Passengers may be asked to turn on a device during security checks, with those which fail to do so being confiscated.

The airport, however, continues to operate as normal despite the increased alert levels in the US.

The move follows a request from the US that “certain overseas airports” implement enhanced security measures.

American officials said last week they were aware of a “credible” terrorist threat, but have not linked the security changes to any specific intelligence.