US Department of Homeland Security secretary Jeh Johnson has revealed that the department is looking at expansion of preclearance operations at additional foreign airports to enhance national security.

The department said in a statement that travellers would now be required to undergo screening before boarding flights entering the US.

The preclearance facilities are staffed and operated by customs and border protection (CBP) officials. Before boarding their aircraft, ship or train, passengers have to go through immigration and customs, public health and department of agriculture inspections to streamline border procedures and reduce congestion at entry points.

Till now, the US operates 15 air preclearance locations in Ireland, the Bahamas, Bermuda and Canada.

"Our goal is to begin formal negotiations for an additional set of preclearance airports in 2015."

An additional facility was opened at the Abu Dhabi International Airport in the United Arab Emirates this year.

Speaking about the need for the preclearance at more foreign airports, Johnson said in a statement: "We should take every responsible opportunity we have to detect and intercept threats before they actually reach the homeland.

"The Christmas Day bombing attempt in 2009 showed us that terrorists may try to conduct attacks on US-bound airplanes even before they’ve landed here.

"Preclearance operations also facilitate lawful travel by reducing the number of passengers who need to clear customs at the largest US airports, which reduces wait times for everyone."

The department stated that last year, about 16 million passengers passed through these preclearance locations. At Abu Dhabi, about 290,000 passengers and crew have been processed so far, which has led to shortening of lines at domestic airports such as JFK and Chicago O’Hare.

In the recent past, 450 people have been denied entry on US-bound aircrafts from Abu Dhabi, which includes some individuals on the terrorism screening database.

The department is working on introducing preclearance operations at additional foreign airports.

"We have initiated a process for foreign airports and host governments to express an interest in preclearance operations and expect responses by the end of this month," Johnson added.

"We are focusing on key airports in Europe and Asia. We are also in productive conversations with CEOs of US airlines, who fully support promoting aviation security. Our goal is to begin formal negotiations for an additional set of preclearance airports in 2015."