The Prime Minister said he hoped the measures would not cause unnecessary delays but stressed that no risks could be taken with passenger safety.
Changes to security measures were announced after Washington Homeland Security Secretary Jeh Johnson ordered beefed-up security at foreign airports that have direct flights to the US, reportedly as a result of intelligence that groups in Yemen and Syria had joined forces to plot an attack.
Mr Cameron told the BBC: "We take these decisions looking at the evidence in front of us and working with our partners.
"This is something we've discussed with the Americans and what we have done is put in place some extra precautions and checks.
"The safety of the travelling public must come first. We mustn't take any risks with that.
"I hope this won't lead to unnecessary delays but it's very important that we always put safety first, and we do."
The increased security measures will include closer scrutiny of personal electronics and foot- wear. These actions come amid fears that individuals with Western passports who have travelled to Syria and Iraq to fight with Islamist extremists could be used to smuggle devices onto planes.
l The Foreign Office yesterday updated its travel advice on Uganda after the authorities in Kampala warned of a possible continuing terror threat at Entebbe Airport.
The advice reads that the Ugandans are "concerned about the possibility of a further attack" and have issued a number of alerts warning of a heightened risk of terrorism.