American Airlines and Delta Air Lines said on Wednesday they are working with law enforcement and airport agencies in the Washington area to ensure the safety of travelers and workers after supporters of President Donald Trump stormed the US Capitol.

American has also increased staffing at Washington-area airports "as a precautionary measure" and will not be serving alcohol on flights to and from the area, a spokesman said.

The comment followed reports of unruly passengers on flights into the DC area on Tuesday ahead of the disruption at the Capitol, raising concern about their departure from the region.

Sara Nelson, president of the Association of Flight Attendants-CWA representing workers at 17 airlines including United Airlines, said the protesters should not be allowed to depart the Washington area on commercial flights after exhibiting "mob mentality behavior" on flights into the region.

"The mob mentality behavior that took place on several flights to the DC area yesterday was unacceptable and threatened the safety and security of every single person on board," she said in a statement.

"Acts against our democracy, our government and the freedom we claim as Americans must disqualify these individuals from the freedom of flight," she said.

United did not immediately comment.

The Transportation Security Administration, which has authority over US travel security, said it is "always on high alert" and has "multiple layers of security in place." It declined to provide details for security reasons.

Hundreds of Trump supporters stormed the Capitol hoping to overturn his election defeat, forcing Congress to postpone a session that would have certified President-elect Joe Biden's victory.

The head of the US Travel Association, Roger Dow, condemned the disruption at the Capitol.

"The behavior we are witnessing has no place in any peaceful democracy, much less in the country that is supposed to be the foremost example of democratic principles," Dow said in a statement.