IS militants stormed late Wednesday night the major towns of Talkif and Qaraqoush, as well as the small towns of Bartella, Bashiqa and al-Guier in east and northeast of Nineveh's provincial capital city Mosul, the source told Xinhua on condition of anonymity.
The attackers seized the towns and announced over loudspeakers that these towns have become part of their self-proclaimed Islamic State, the source said.
The move of the IS militants forced thousands of mainly Christian residents to leave their homes to safer areas, the source added.
The latest fall of towns into the hands of the militants came amid fierce clashes between the Kurdish Peshmerga security forces and Islamic State militants.
The Kurdish Peshmerga forces have launched a major offensive to fight back the IS militants who seized earlier many towns in Nineveh, including the large town of Sinjar, some 100 km west of Mosul, which is the home of the Yazidi minority.
The Peshmerga has since retaken control of some villages and part of Sinjar, but so far the Kurds have apparently failed to take full control of the town and the other areas seized earlier by the IS militants.
The latest battles forced thousands of Iraqi families to leave their homes and now are in immediate need of urgent assistance.
On Tuesday, the United Nations Children's Fund (Unicef) said in a statement that up to 40 children from displaced families of the Yazidi minority, who have moved to a nearby mountain, were reported to have died.
"According to official reports received by the Unicef, these children from the Yazidi minority died as a direct consequence of violence, displacement and dehydration over the past two days," the statement said.
The battlefields of Talkif, Qaraqoush, Sinjar are part of disputed areas which are ethnically mixed with Kurds, Arabs, Turkmens and others.
The Kurds have demanded expansion of their autonomous region in northern Iraq to include the oil-rich province of Kirkuk and other areas in the Iraqi provinces of Nineveh, Salahudin and Diyala, but their move is being fiercely opposed by the central government in Baghdad.
Early in June, the Peshmerga took control of the disputed areas, including the northern city of Kirkuk after the Iraqi security forces abandoned their bases following the IS's June 10 blitzkrieg across Iraq in which the Al Qaeda offshoot and other Sunni militant groups seized large swathes of territories in predominantly Sunni provinces.