Sen. Barbara BoxerBarbara Levy BoxerThe ‘bang for the buck’ theory fueling Trump’s infrastructure plan Kamala Harris endorses Gavin Newsom for California governor Dems face hard choice for State of the Union response MORE (D-Calif.) urged the United Nations to help evacuate thousands of Yazidi people trapped by Islamic State in Iraq and Syria (ISIS) militants on Mount Sinjar in Iraq.

“I am deeply concerned about the humanitarian crisis in Iraq and the dire situation of the Yazidi people trapped by ISIS militants on Mount Sinjar,” Boxer wrote in a letter Tuesday to Secretary General Ban Ki-moon. “I urge you to support the establishment of a humanitarian corridor to evacuate Yazidis who are sick and dying.”

Boxer said the U.N. should continue to work with the United States, which has already launched humanitarian operations and airstrikes to combat ISIS fighters. She said because of their efforts more than 20,000 Yazidis have escaped Mount Sinjar, but more are still trapped.

The Yazidis are trapped on the mountain due to the expansion of the extremist group ISIS, which has seized land in Iraq and Syria.

In her letter, Boxer cited reports that ISIS has killed at least 500 Yazidis and more are still at risk.

“With thousands more Yazidis remaining on the mountain range, it is clear more must be done to protect these innocent men, women, and children,” Boxer wrote. “I understand that the U.N. is working to establish a humanitarian corridor to allow more Yazidis to escape. I urge you to move expeditiously to support such a corridor that would provide multiple safe routes for the Yazidis.”