Given an ultimatum by the Islamic State to either convert to Islam, pay a security tax, get killed or leave their homes, tens of thousands of ethnic Kurds in northern Iraq have taken the fourth option with as many as 200,000 Yazidi Iraqis fleeing the towns of Sinjar, Wana and Zumar, the New York Times reported Sunday. The ultimatum was issued as the Islamic State of Iraq and Syria, or ISIS, claimed it gained control of “more important areas which were controlled by the [Kurdish] peshmerga [forces] and the secular militias.”

“Thousands of Yazidi people have been killed,” Jawhar Ali Begg, a spokesman for the Yazidi Kurdish community, told the Associated Press, which reported that 40,000 Iraqis fled the towns.

The fleeing of at least 40,000 northern Iraqis is in addition to the more than 1.4 million Iraqis that the United Nations said last month have been displaced by fighting since the beginning of the year.

On Sunday, the Islamic State, the militant group formerly known as ISIS, which claimed it created a caliphate using territory it controlled in Iraq and Syria, seized Zumar, a town with oil fields near the Syrian border, from Kurdish forces, security officials and Zumar residents told the Times. The group then took control of Sinjar, in northwestern Iraq. The town has a large number of Yazidis, who practice a religion that combines Islam and ancient Persian religions and that ISIS considers “apostates,” according to the Times.

The Islamic State then moved on to Wana, a northwestern Iraqi town of strategic importance because it’s near the Mosul Dam, which supplies electricity and water to Iraq. Wana sits near the Tigris River and is about 30 miles from Mosul, Iraq's second-largest city, which was captured by ISIS in June.

"The situation has taken a turn for the worse over the weekend," Karwan Zebari, an official with the Kurdistan regional government's office in Washington, D.C., told Reuters. He added that peshmerga forces were planning a counter-offensive to take back the seized towns.