Kelly made his remarks during the Memorial Day weekend, one of the busiest travel periods in the United States, 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 -- may be planned.

"There's a real threat -- numerous threats against aviation," Kelly told the Fox News Sunday program when asked about the likelihood a wide-reaching ban on large electronics in airplane cabins could be imposed.

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," the homeland security chief said.

But in an interview on NBC's "Meet the Press" later, Kelly specified that despite ongoing and persistent concerns, "we have no specific threats right now."

Read also: Airlines fret about laptop ban from Europe during peak season

A laptop ban could disrupt travel between Europe and America. Some 3,250 flights a week are expected this summer between European Union countries and the United States, according to aviation industry figures.

If put in place, a laptop ban would greatly expand on a rule Kelly announced in March banning electronic devices larger than a smartphone from the cabins of flights from 10 airports in the Middle East and North Africa.

The rule affects Turkey, Jordan, Egypt, Saudi Arabia, Kuwait, Qatar, the United Arab Emirates and Morocco.

Britain took similar measures in March 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.