Embattled FBI director Kash Patel has denied under oath allegations of excessive drinking and unexplained absences on the job, dismissing them as “baseless” during a fiery congressional hearing.

Patel sought to push back as Democrats challenged him over the “extremely alarming” reports, which ran in the Atlantic, which they argued would a mount to a “gross dereliction” of duty.

The FBI director has sued the magazine, and the author of a story it published, filing a defamation lawsuit in US district court for the District of Columbia that seeks $250m in damages.

“It’s a total farce. I don’t even know where you get this stuff,” Patel told Chris Van Hollen, ranking member of the Senate appropriations subcommittee, after he asked about the claims reported by the Atlantic. “I will not be tarnished by baseless allegations.”

When Van Hollen asked if Patel would be willing to take a test to determine whether he has a drinking problem, the FBI director snapped that he would – provided the senator would take it alongside him.

In his opening remarks, Van Hollen said: “What we are learning about what’s happening at the FBI is anything but normal. When your private actions make it impossible for you to perform your public duties, we have a big problem … these reports about your conduct, including reports you’re being so drunk and hungover that your staff had to force entry into your home are extremely alarming, if true, they demonstrate a gross dereliction of your duty and a betrayal of public trust.”

The Atlantic reported that Patel’s alcohol consumption had become “a recurring source of concern across the government”, citing interviews with more than two dozen people, including current and former FBI officials.

The most serious allegations include that his security detail on at least one occasion struggled to rouse him because he appeared intoxicated, and that agents had sought “Swat-level breaching equipment” to gain access to a room where he was unresponsive behind a locked door.

Patel has forcefully denied the allegations. “Print it, all false, I’ll see you in court – bring your checkbook,” he told the magazine. The Atlantic has said it stands by its allegations.