Islamic State militants are surrounding and threatening to execute 300 Yazidi families in northern Iraq, according to Yazidi sources.

Unconfirmed reports from Reuters news agency say the members of the minority Yazidi religion were threatened after Islamic State (or Isis) threatened to slaughter them unless they convert to Islam.

The families had fled to Mount Sinjar in the Iraqi north-west region to escape from the Islamic State's invasion,

The families in the villages of Koja, Hatimiya and Qaboshi are surrounded by the Sunni militants who are mounting an offensive through northern Iraq, which has sent tens of thousands of Yazidis and Christians fleeing for their lives, prompting international outrage.

The UN has said that roughly 40,000 people – many women and children – have taken refuge in nine locations on Mount Sinjar.

Local officials said that at least 500 Yazidis, including 40 children, have been killed over the past week, and many more have been threatened with death.

Roughly 130,000 residents of the Yazidi stronghold of Sinjar have fled to Dohuk, in Iraqi Kurdistan to the north of Iraq, or to Irbil in the Kurdistan Region.

Syrian Kurdish officials say thousands of Yazidis have fled across the border from Iraq.

The Associated Press reported on Saturday that they fled after Kurdish fighters were able to open a safe passage into Syria, following clashes with the Islamic State group.

On Saturday the US launched airdrops to aid the trapped Yazidis. US president Barack Obama warned it is "going to take some time" for the US to help Iraqis overcome the jihadist-led Sunni rebellion and stabilise their country. Revamping and resupplying the military would be a "long-term project", he added.

In Germany, on 9 August, members of the Yazidi community held a demonstration in protest at the persecution of Yazidis in Iraq.