Oil Ministry spokesman Assem Jihad said Kurdish troops known as peshmerga also expelled the local workers from the Bai Hassan and Kirkuk oil fields. He declared the takeover "a violation to the constitution" and warned that it poses "a threat to national unity."
There was no immediate comment from authorities in the Kurdish self-rule region of northern Iraq.
The already difficult relationship between the Kurds and Iraq's central government has sharply deteriorated in recent days. On Wednesday, Prime Minister Nouri al-Maliki accused the Kurds of harboring the Sunni militants who have overrun much of the country over the past month. A day later, authorities suspended all cargo flights to the Kurdish region's two main airports.
The Kurds have responded by declaring their politicians will boycott Cabinet meetings and renewing demands that al-Maliki step down. The seizure of the two oil fields, however, is a decidedly bigger step, and could signal a quicker unraveling of relations between the Kurds and al-Maliki.
Associated Press writer Maamoun Youssef in Cairo contributed to this report.