There are "far fewer" Yazidi refugees marooned on Mount Sinjar in northern Iraq than previously thought and they are in better condition than expected, the Pentagon said Wednesday.

"Based on this assessment, the interagency has determined that an evacuation mission is far less likely," Pentagon press secretary Rear Admiral John Kirby said in a statement after US troops were flown onto the mountain to see the refugees' plight firsthand.

The UN refugee agency has said tens of thousands of civilians, many of them members of the Yazidi minority, remain trapped on the mountain by jihadists from the so-called Islamic State (ISIL), which has overrun large swaths of Iraq and Syria in a lightning and brutal offensive.

Kirby stressed that the US troops who saw for themselves the civilians stranded on the mountain did not engage in any combat.

Last week, President Barack Obama authorized air strikes to protect Yazidi refugees and US personnel in Arbil, the capital of Iraq's autonomous Kurdish region, but he too has insisted that US "combat troops" will not return to war in the unstable nation.

"The team, which consisted of less than 20 personnel, did not engage in combat operations, and all personnel have returned safely to Arbil by military air," Kirby said of Wednesday's assessment.

"The team has assessed that there are far fewer Yazidis on Mount Sinjar than previously feared, in part because of the success of humanitarian air drops, air strikes on ISIL targets, the efforts of the Peshmerga and the ability of thousands of Yazidis to evacuate from the mountain each night over the last several days.

"The Yazidis who remain are in better condition than previously believed and continue to have access to the food and water that we have dropped."