Kelly made his remarks during the Memorial Day weekend, one of the busiest travel periods in the US, and at a time when the bombing at a concert in Manchester, England has raised concerns that further attacks -- possibly involving explosives packed in electronic devices -- might be planned.
"There's a real threat -- numerous threats against aviation," Kelly told the Fox New Sunday program, when asked about the likelihood that a wide-reaching ban on large electronics in airplane cabins could be imposed.
The US homeland security chief said terrorists are "obsessed" with the idea of "knocking down an airplane in flight -- particularly a US carrier, if it's full of mostly US folks."
A ban could seriously disrupt flights between Europe and the US. Some 3,250 a week are expected this summer between European Union countries and the US, according to aviation industry figures.
If the laptop ban Kelly discussed is put in place, it would greatly expand on a rule he announced March 21, banning electronic devices larger than a smartphone from the cabins of flights from 10 airports in the Middle East and North Africa.
Countries affected by that rule are Turkey, Jordan, Egypt, Saudi Arabia, Kuwait, Qatar, the United Arab Emirates and Morocco.
In March, Britain took similar measures targeting a smaller list of countries: Turkey, Lebanon, Jordan, Egypt, Tunisia and Saudi Arabia.
In Europe last week, during President Donald Trump's nine-day foreign trip, Kelly met with European Commission officials in Brussels to discuss a possible laptop ban in airplane cabins.
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