At what non-preclearance airports are there US DHS officers?

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I've read that at certain airports (especially London airports), there are sometimes American DHS officers doing spot checks of passengers about to board flights to the US.
At what airports is this the case?
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Is there Border Patrol in airports?
There are two immigration agencies that operate at airports. One is Customs and Border Protection, which places agents at all international airports. The other is the U.S. Border Patrol, which falls under the umbrella of CBP. Border Patrol agents work mostly in airports that are within 100 miles of the border.Is there US immigration at Doha airport?
No you cannot. Immigration can only be done after landing in USA. In Abu Dhabi airports these service is available,i heard that Qatar airways will provide that.Does Abu Dhabi airport have US immigration?
The United States Customs and Border Protection (CBP) facility at Terminal 3 in Abu Dhabi International Airport is a purpose-built facility that allows U.S. bound passengers to undertake all immigration, customs and agriculture inspections in Abu Dhabi, prior to departure.Is SXM pre cleared?
Re: Clear Customs in SXM or USA? Sorry, no US preclearance on Sint Maarten.How Illegal Items Are Found And Destroyed At JFK Airport
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