WASHINGTON (CNN) -- Two senior Democratic senators demanded on Tuesday that the United States stop force-feeding certain detainees at the Guantanamo Bay, Cuba, detention facility, a public stand that added to a rising chorus of protest over their treatment.

Sens. Dianne Feinstein of California, who chairs the Intelligence Committee, and Richard Durbin of Illinois, the Democratic whip, registered their strong opposition to the practice during the confirmation hearing of James Comey to become the next FBI director.

"This is inhumane," Feinstein said, noting that she wrote Defense Secretary Chuck Hagel about the matter but hadn't heard back.

Feinstein traveled to Guantanamo in June with Republican Sen. John McCain of Arizona and White House Chief of Staff Denis McDonough, where she said she "took a look" at the force feeding issue.

"I'm very concerned about it because it's the wrong thing to do," she said.

"Detainees are restrained in a chair by body, by foot, by hand, and twice a day a tube is inserted, perhaps covered with olive oil, up the nose and down into the stomach. And the individual is force fed. This goes on week after week and month after month," Feinstein said.

Durbin said that he agreed with Feinstein and promised action.

"We're going to join together, and perhaps others wish to join us in a letter to the president asking him to exercise his executive authority to end this force feeding in Guantanamo," he said.

There are 166 prisoners at Guantanamo, which was established to house terror suspects following the 2001 al Qaeda attacks on the United States and the start of the Afghan war, and 106 have been on hunger strikes since early this year. More than 40 have been force-fed, military officials said.

On Monday, a federal judge in Washington rejected a bid by detainees to end force-feeding during the holy month of Ramadan, saying the court lacked jurisdiction.

But U.S. District Judge Gladys Kessler urged President Barack Obama to do something about it, calling it a "painful, humiliating, and degrading process."

The government has said force-feeding provides "essential nutrition and medical care."

When asked about Kessler's comments, White House spokesman Jay Carney told CNN's Jessica Yellin that he would defer to the Defense Department and Justice Department.

But Carney said the president continues to believe the facility should be closed.

Separately, rapper Yasiin Bey, better known to many as Mos Def, has said he voluntarily attempted the standard procedure for force-feeding Guantanamo detainees.



Warning: Images in this video may be distressing to viewers

The aborted procedure was captured in a four-and-a-half-minute video commissioned by human rights organization Reprieve, with the intent of raising awareness and support for detainees.