Iran warned on Sunday that independence for Iraqi Kurdistan would mean an end to all border and security arrangements with the regional government.
"Border agreements stand only with the central government of Iraq, and secession of Kurdistan region from the central government of Iraq would mean the blocking of all shared border crossings," Ali Shamkhani, secretary of Iran's Supreme National Security Council, told the state broadcaster IRIB.
"The secession of the Kurdistan region from Iraq's territory would be the end of security and military agreements between Iran and the Kurdistan region," he added.
The leaders of Iraq's autonomous Kurdish region are set to hold a referendum on independence on September 25.
Although the referendum would not be legally binding, Shamkhani said that any move towards independence could lead to Iran disregarding rules of engagement along the border.
"Iran would then prepare itself to enter areas deeper than the border in response to anti-security actions," he said, referring to regular attacks by Iran's own Kurdish separatists based in Iraqi territory.
Tehran, which has worked closely with Kurdish Peshmerga forces in Iraq against the Islamic State group, fears the independence movement could encourage separatists among its own Kurdish population.
Shamkhani repeated the official line that Iran would only ever recognize the "united, integrated and federal government of Iraq".
Iraq's Kurds have also come under intense diplomatic pressure from the United Nations, United States and neighboring Turkey to cancel the referendum amid fears it will add yet another source of conflict to the combustible region.