New visa plan for Yemeni passengers at UK airports
All Yemeni citizens travelling through the UK on long-haul flights will need a visa, even if they are in transit, it has been announced.
Home Secretary Theresa May said Yemen was of "real and pressing concern to the international community".
From Thursday, Yemeni citizens need a visa before travelling to the UK, even if they are in transit and planning to arrive and leave from the same airport.
On Monday, the UK terror threat level reduced from "severe" to "substantial".
Mrs May said that since the introduction of the Direct Airside Transit Visa (DATV) regime, a number of countries had been added to a list of those requiring clearance.
"This has been done in response to emerging counter-terrorism threats to the UK," she said.
"Recent events have highlighted Yemen as being of real and pressing concern to the international community.
"We feel that imposing a DATV regime on those Yemeni citizens who are travelling through the UK is a sensible and proportionate response to the threat."
The Detroit bomber, who tried to blow up an aeroplane on Christmas Day 2009, was trained in Yemen, Mrs May said.
And bombs disguised as toner cartridges which were found on board planes at East Midlands airport and in Dubai last October were also sent from Yemen, she added.
Mrs May this week reduced the terror threat level for the UK.
The new alert level meant the risk of a terrorist attack was considered to be a "strong possibility" and "might well occur without further warning"," she said.
"The change in the threat level does not mean that the overall threat has gone away," added Mrs May.
"There is still a real and serious threat to the UK and I would ask the public to remain ever vigilant."