ANKARA (Reuters) - The head of Turkey s nationalist opposition said on Thursday a planned independence referendum by Kurds in northern Iraq should be viewed by Ankara as a reason for war  if necessary . Turkey, which is battling a three-decade Kurdish insurgency in its southeast, is concerned the referendum could further stoke separatist sentiment among the 15 million Kurds in Turkey.  On Wednesday, Foreign Minister Mevlut Cavusoglu visited Iraq, where he conveyed to Iraqi Kurdish leader Massoud Barzani Ankara s concerns about the decision to hold the referendum, planned for Sept. 25. Nationalist Movement Party (MHP) leader Devlet Bahceli, who allied with the government in supporting the ruling AK Party s campaign in April s referendum on boosting President Tayyip Erdogan s powers, called on Ankara to oppose the vote.  A position must be taken to the end against Barzani s preparation for an independence referendum which incorporates Turkmen cities,  Bahceli told a news conference in Ankara.  This is a rehearsal for Kurdistan. If necessary Turkey should deem this referendum as a reason for war,  he added. Bahceli does not set policy, though his ideas reflect those of a segment of Turkish society fiercely opposed to the idea of an independent Kurdistan and supportive of Iraq s Turkmen ethnic minority, which has historical and cultural ties to Turkey. Kurds have sought an independent state since at least the end of World War One, when colonial powers divided up the Middle East and left Kurdish-populated territory split between modern-day Turkey, Iran, Iraq and Syria.     Like Turkey, Iraq, Iran and Syria all oppose the idea of Iraqi Kurdish independence, fearing it may fuel separatism among their own Kurdish populations.  The Kurdistan Workers Party (PKK) militant group, deemed a terrorist organization by Ankara, the United States and European Union, has waged a 33-year insurgency in southeast Turkey in which more than 40,000 people have been killed. The United States and other Western nations fear September s vote could ignite a new conflict with Baghdad and possibly neighboring countries, diverting attention from the war against Islamic State militants in Iraq and Syria. 