About 100,000 Kurds have fled Kirkuk, fearing unrest, since Monday's takeover of the region by Iraqi forces, officials from the semi-autonomous Kurdistan Regional Government (KRG) said on Thursday.

About 18,000 families have taken shelter in the cities of Erbil and Sulaimaniya, the governor of Erbil Nawzad Hadi told reporters. One of his aides told Reuters the total number of people was about 100,000.

In a "major, multi-pronged" attack, Iraqi federal troops seized several parts of the disputed Kurdish-controlled province of Kirkuk after Iraqi Kurds voted for independence in a referendum late last month.

Tensions have soared since the Kurds held a non-binding referendum last month in which they voted for independence from Iraq. The central government, along with neighboring Turkey and Iran, rejected the vote.

The Iraqi government and the autonomous Kurdish region in the north have long been divided over oil revenues and the fate of disputed territories like Kirkuk that are controlled by Kurdish forces but are outside their self-ruled region

The Kurds assumed control of Kirkuk, in the heart of a major oil-producing region, in the summer of 2014, when IS militants swept across northern Iraq and the country's armed forces crumbled. Baghdad has demanded the Kurds withdraw.