President Recep Tayyip Erdoğan said Monday that Turkey considers the independence referendum in northern Iraq's Kurdistan Regional Government (KRG) null and void and illegitimate regardless of its results, adding that there may be economic and military repercussions.

Speaking at a forum in Istanbul, Erdoğan stated that the Habur border gate with Iraq, which serves as the KRG's main gateway to the world, is only open for Turkey-bound traffic, and signaled that it could be totally closed in the future.

Erdoğan also warned that Turkey could block the KRG's oil exports. "We'll see who KRG will sell its oil to, Turkey is in control of the valve," he said, referring to the Kirkuk - Ceyhan oil pipeline that connects oil fields in northern Iraq to the oil terminal in the Mediterranean.

Oil revenues are of crucial importance for the KRG's economy, which is suffering from a high rate of unemployment.

Erdoğan noted that Turkey would not hesitate to use force if necessary, saying "Just as we've liberated Jarablus, al-Rai, and al-Bab from Daesh in Syria, if need be we won't shy away from such steps in Iraq."

"We may come there overnight all of a sudden," he said sternly.

Last week the Turkish Armed Forces began a military drill in the region around the border town of Silopi including 100 military vehicles, which continued with reinforcements this weekend.

"We are taking and will take all the steps on political, economic, trade and security fronts. The armed forces did not take necessary steps in Silopi for no reason. There is no compromise," Erdoğan promised.

The Turkish parliament on Saturday approved overwhelmingly a one-year extension of a mandate to use troops abroad in Syria and Iraq.

Monday's non-binding referendum will see voters in northern Iraqi Kurdish Regional Government (KRG)-held areas, including areas disputed between Irbil and Baghdad such as oil-rich Kirkuk, vote on seceding from Iraq.

Baghdad, Turkey, Iran, the U.S., and the UN have all spoken out against the poll, saying it will only distract from the ongoing fight against Daesh and further destabilize the region.

Iraq's central government has threatened to intervene militarily if the vote leads to violence.

KRG President Massoud Barzani has said a "Yes" win would not result in an automatic declaration of independence but would simply lead to further negotiations with Baghdad.