Turkish President Recep Tayyip Erdogan said on Monday that Ankara would close its border with northern Iraq over an independence referendum and threatened the Iraqi Kurds with blocking their key oil exports.
"Entrance-exit will be closed" at the Habur border crossing, Turkey's sole land border crossing with Iraq, Erdogan said in a speech in Istanbul.
He said there were currently crossings allowed to the Iraqi side only but travel would be closed in both directions this week.
He added: "After this let's see through which channels they will send their oil through... and who they will sell to. The valve is with us. It's finished the moment we close it."
Iraqi Kurdish oil is exported through Turkey and its southern Ceyhan port, a key economic lifeline for the region.
Although Turkey enjoys strong ties with the Kurdistan Regional Government (KRG), Ankara fears the vote could raise separatist aspirations among its own sizeable Kurdish minority, the largest in the region.
Iraqi Kurds were voting on Monday in defiance of warnings from Ankara as well as Baghdad and Iran. But Erdogan said "irrespective of the result, we see this as null and void and say it is illegitimate".
He again urged the KRG to take a step back and appeared to threaten the northern Iraq administration of a possible cross-border operation.
"In Iraq, when necessary, we will not shy away from taking these types of steps," Erdogan said, referring to Turkey's military operation launched last year in Syria against Islamic State extremists and Syrian Kurdish militia.
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," Erdogan promised.
The Turkish parliament on Saturday approved overwhelmingly a one-year extension of a mandate to use troops abroad in Syria and Iraq.
Earlier Turkish Prime Minister Binali Yildirim said Ankara would take steps with regard to air space "before it is too late" although flights to northern Iraq from Turkey are reported to be running as normal.