Syrian, Libyan and Egyptian citizens will in future have to apply for a visa if they are travelling through UK airports.
The three countries, which have seen major upheaval following a wave of domestic protests, have been added to the list of nations covered by the Direct Airside Transit Visa requirements.
Introduced in response to threats to national and border security, they covers passengers who are only in the UK to change flights and never leave the airport.
Home Secretary Theresa May told MPs: “We see this as a necessary measure to protect the security of our borders.
“The situation in Syria continues to pose a serious concern to us and the wider international community.
“Libya and Egypt are emerging from a period of instability.”