Navy officials briefed three U.S. senators Wednesday on reported naval encounters with unidentified flying objects.

Democratic Sen. Mark Warner, the vice chairman of the Senate Intelligence Committee, was among those briefed. His office confirmed the briefing to POLITICO .

“If pilots at Oceana or elsewhere were reporting flight hazards that interfere with training or put them at risk, then Senator Warner wants answers,” Rachel Cohen, his spokeswoman told CNN . “It doesn’t matter if it’s weather balloons, little green men, or something else entirely — we can’t ask our pilots to put their lives at risk unnecessarily.”

Navy pilots have reported strange objects during their flights for years. In an interview with the New York Times, five airmen said that, in 2014 and 2015, they saw unusual aircraft flying at 30,000 feet over the East Coast with no visible engine or infrared exhaust plumes. Other pilots encountered aircraft that appeared to defy the laws of aerodynamics.

The U.S. Navy updated its UFO reporting guidelines in April in response to an increase in sightings and reports of intrusion into sensitive military operations. Prior guidelines often left reports uninvestigated.

“There have been a number of reports of unauthorized and/or unidentified aircraft entering various military-controlled ranges and designated airspace in recent years,” Navy officials told POLITICO . “The Navy is updating and formalizing the process by which reports of any such suspected incursions can be made to the cognizant authorities.”

These strange sightings have been a particular subject of interest for lawmakers.

Former Senate Majority Leader Harry Reid secured funding in 2009 for the Advanced Aviation Threat Identification Program that spent nearly $20 million on research of “unidentified aerial phenomena.” The program ran until 2012. In late 2017, the Pentagon set up another program to help study the reports.

This classified briefing comes as President Trump has expressed skepticism toward the issue.