A renewed offensive by the Islamic State (IS) against Iraq's Yazidi minority population is likely to be attempted genocide, a UN official has warned.

The extremist group advanced towards northeastern Mount Sinjar on Monday, attacking Yazidi areas and sending residents fleeing.

Ivan Simonovic, the UN assistant secretary-general for human rights told reporters on Tuesday that evidence suggested "[IS] actions against Yazidis may amount to attempted genocide."

Thousands of Yazidis are still stranded on the mountain, where they fled to escape IS attacks on the area in August that killed hundreds and displaced tens of thousands. Yazidis follow an ancient religion incorporating elements of Islam and indigenous beliefs, but IS views them as "devil worshippers."

It was that crisis which led US President Barack Obama to begin airstrikes on IS targets in Iraq, in order to halt their advance on Sinjar and avert a feared humanitarian catastrophe. The US also dropped aid to those seeking refuge on the mountain.

Since then evidence of atrocities perpetrated by IS against Yazidis has mounted. The group massacred hundreds of men and boys in the Sinjar region and kidnapped hundreds more women and children, according to Amnesty International.

The US provided similar assistance more recently to the Syrian border town of Kobane, which is currently besieged by IS. American aircraft have carried out more than 135 airstrikes in the area since it extended operations into Syria in September, according to US Central Command (CentCom).

Earlier this week American aircraft airdropped arms to the Kurdish People's Protection Units (YPG) fighters defending the town. However, the Pentagon is currently investigating whether some may have fallen into IS hands. Pentagon Press Secretary Rear Adm. John Kirby said at a press conference on Tuesday that its analysts were trying to work out what had happened.

American C-130 planes delivered 27 bundles of weapons, ammunition and medical supplies provided by Iraq's Kurdistan Regional Government (KRG) to YPG fighters at dawn on Sunday, according to a CentCom statement. A video posted on YouTube on Tuesday by a group calling itself "A3maq News" purports to show some of the airdropped supplies in the hands of the extremist group. The footage shows a masked and armed militant examining a package attached to a parachute. Later, he looks into crates containing various munitions, including RPG rounds and grenades.

CentCom confirmed in a statement on Monday that one airdropped bundle had missed its target. However, it said it had subsequently been destroyed in a follow-up airstrike to stop it falling into enemy hands.

Kirby said that he could not confirm if the video was authentic or not: "They are certainly of the kinds of material that was dropped... so it's not out of the realm of the possible in that regard," he said, according to the BBC.

The "A3maq News" group that uploaded the video has previously posted IS-linked content and some of the weapons seen in the video appear to match those possessed by Iraq's Kurdistan Regional Government (KRG), which supplied the arms.

Airdrops don't always make their marks. US Defence Secretary Chuck Hagel said in August that around 80 percent of aid dropped on Mt. Sinjar reached its target.

Kobane is surrounded on three sides by IS and is bordered to the north by Turkey. The airdrops were apparently a response to the Turkish government's refusal to grant repeated requests to open a land corridor allowing humanitarian and military supplies into the town.

However, on Monday Ankara announced that it would allow Iraqi Kurdish fighters to cross the border. KRG lawmakers were to vote on Wednesday on whether the semi-autonomous region's peshmerga troops should be deployed to Kobane, a move which would effectively bring the Iraqi Kurdistan directly into the Syrian civil war.

The battle for Kobane has raged since IS launched a major offensive last month. Taking the town would be a major propaganda victory for IS and also allow the extremist group to connect territory held in the Syrian province of Aleppo with its stronghold of Raqqa further east. It would also give IS control over a large stretch of the Turkish border.