A US mission to evacuate Iraqi civilians trapped on a mountain by the Islamic State group is far less likely after a US assessment team sent there found the humanitarian situation was not as bad as feared, the Pentagon said.

A team of US military and humanitarian aid personnel, who flew to the Sinjar Mountains in northern Iraq under cover of darkness to assess the situation of thousand of members of the Yazidi religious minority, found far fewer people and in better condition than expected, the Pentagon said in a statement.

"Based on this assessment," the Pentagon said, "an evacuation mission is far less likely."

The Pentagon credited the better-than-expected situation on air drops of food and water, US airstrikes on Islamic State group targets, efforts of Kurdish Peshmerga fighters and the ability of thousands of Yazidis to evacuate the mountain in recent nights.

The White House said earlier the United States had not ruled out using American ground forces in an operation to extract the trapped civilians, but added the troops would not engage in combat.

The team of fewer than 20 US personnel flew early on Wednesday morning to the mountains, a defence official told Al Jazeera, before returning safely to the Iraqi Kurdistan capital of Erbil by military air transport.

The United States has 130 military personnel in Erbil.

Obama is expected to make a decision in days on the strategy of what the US calls a humanitarian operation that some thought could have included airlifts and creating safe passages executed by US ground troops.

"We don't believe that involves US troops re-entering a combat role in Iraq," Ben Rhodes, Obama's deputy national security adviser, had said.

"It involves frankly a very difficult logistical challenge of moving folks who are in danger on that mountain into a safer position."

But Hillary Mann Leverett, former White House and State Department official and professor, told Al Jazeera that the US intervention has more to do with state interests than helping Yazidi Kurds.

"In fact, Oxfam said today that there are 28 million people. The largest number of people in Oxfam's historic memory that are dependant on aid; that are in dire need of aid across the Middle East in conflicts in Iraq, Gaza, Yemen and Jordan and Syria - and the US doesn't go in to airlift all these people out," said Leverett.

She said that the operation deserves more scrutiny than what it has gotten so far, adding that it was about the thousands of non-diplomatic personnel in Baghdad and Erbil, including businessmen with oil giants Chevron and Exxon Mobil.

Obama has been deeply reluctant to revive any military role in Iraq after withdrawing the last combat troops in 2011 to end eight years of costly war that eroded the United States' reputation around the world.

Drone attack

The US has been delivering food and water to the refugees for several days. But Rhodes said it was unsustainable to let thousands of people remain on the mountain.

"There needs to be a lasting solution that gets that population to a safe space where they can receive more permanent assistance," Rhodes said.

On Wednesday, a US drone attacked and destroyed an armed truck operated by fighters from the Islamic State group near Sinjar, the US Central Command said.

US and British military forces have been dropping supplies of food and water to those on Mount Sinjar in the last week and Rhodes said other countries - including Australia, Canada and France - were also offering to help.

UN agencies have rushed emergency supplies to the Dohuk region by the Syrian and Turkish borders, where the office of the UN High Commissioner for Refugees says about 400,000 refugees have fled, including Yazidis, Christians and other minorities.