People wait in long TSA security lines at John F. Kennedy International Airport (JFK) in the Queens borough of New York on Monday. (AP Photo/Ryan Murphy)

NEW YORK (AP) — Armed federal immigration officers in tactical gear moved through terminals at some of the busiest U.S. airports Monday, standing near security lines and checkpoints after President Donald Trump ordered their deployment during a partial government shutdown that has disrupted air travel nationwide.

The Trump administration said they would supplement Transportation Security Administration staffing at certain airports but provided few details about exactly what they would be doing. Still, after intensified immigration enforcement and protests in cities across the country over the past year, their presence has unsettled some travelers and raised new questions.

On Monday, Associated Press journalists observed Immigration and Customs Enforcement officers and agents patrolling terminals and lingering near long lines of passengers at Hartsfield-Jackson Atlanta International, John F. Kennedy International in New York, Newark Liberty International in New Jersey, George Bush Intercontinental in Houston and Louis Armstrong International outside New Orleans. A handful of other airports — including Phoenix’s Sky Harbor International — also confirmed ICE would be on-site. Chicago Mayor Brandon Johnson said his office was monitoring the deployment of federal officers at O’Hare International.

Federal law enforcement officers are a routine presence at international airports. Customs and Border Protection officers screen arriving passengers, and Homeland Security Investigations agents conduct criminal inquiries tied to cross-border activity. But immigration agents are rarely visible at TSA checkpoints, the front line of domestic air travel.

Monday’s deployments came as hundreds of thousands of Homeland Security workers, including from the TSA, have worked without pay since Congress failed to renew DHS funding last month.

Funding for the department lapsed Feb. 14, when Democrats refused to fund ICE as well as Customs and Border Protection without changes to their operations after federal officers shot and killed Alex Pretti and Renee Good in Minneapolis. But, while routine funding used to pay TSA agents has lapsed, ICE and other immigration enforcement personnel are still receiving paychecks amid the shutdown — a result of Trump’s big tax cuts bill that became law last year.

Meanwhile, the budget stalemate impacting TSA only deepened as Trump rejected the latest offer, this one from his own Republican Party, after a weekend of negotiations.

White House staff pitched Trump on the idea of funding DHS, except for immigration operations that have been central to the dispute, according to a person a familiar with the situation who spoke on the condition of anonymity to discuss private talks. Still, Trump rejected that plan and later escalated his demands that senators also approve the so-called SAVE America Act, a strict proof-of-citizenship voting bill that has essentially no chance in the Congress.

On Monday, the White House also turned down a request from top Democratic negotiator, Sen. Patty Murray of Washington, to meet and continue talks, according to another person granted anonymity to discuss the private conversations.

Democrats are continuing to demand major changes to federal immigration operations — including policy changes that would require ICE officers to get a warrant from a judge before forcefully entering homes, to no longer allow officers to wear masks and to require that they provide clear identifying information on uniforms.

Unlike many recent immigration operations in U.S. cities, where federal agents have often worn face coverings, ICE officers at airports appeared to be largely not masked Monday, following an earlier direction by Trump.