WASHINGTON — On the heels of a travel alert from the U.S. State Department about an increased threat of terrorism, airports nationwide are on high alert during the busy holiday season.

At Reagan National Airport, some officers patrol terminals with K9s, while others carry semi-automatic rifles.

“We have a robust security infrastructure. Some of that is visible to the public, some of that is behind the scenes,” says Chris Paolino, airport spokesman.

“We’re in constant coordination with our federal and local partners. As they provide information, we respond appropriately,” he says.

With the extra holiday traffic and longer security lines, airline passengers are urged to arrive at least two hours ahead of their flight. And as they make their way through airports, they are being asked to stay extra vigilant.

“If you see something that seems out of the ordinary, let us know,” Paolino says.