BERLIN (Reuters) - Germany said on Thursday it was concerned plans by Iraq's autonomous Kurdish region to vote on independence in September, could exacerbate tensions in Iraq.

Comments by Foreign Minister Sigmar Gabriel marked the first international response to Kurdish leader Massoud Barzani's announced plans for a referendum to take place on Sept. 25.

Barzani heads the autonomous Kurdistan Regional Government in Iraq.

"We can only warn against one-sided steps on this issue. The unity of Iraq is on the line," Gabriel said in a statement. "Redrawing the lines of the state is not the right way and could exacerbate an already difficult and unstable situation, in Erbil as well as Baghdad."

Germany is a major partner for the Iraqi Kurds. It has provided 32,000 assault rifle and machine guns, as well as other weapons valued at around 90 million euros since September 2014. About 130 German soldiers are based in Erbil where they are providing training to the Peshmerga, Kurdish fighters.

"I call on all sides to seek dialogue, to find consensus for dealing with open questions, and not to reignite conflicts in the disputed areas of Erbil and Baghdad," Gabriel said.

He said it was imperative to maintain unity within Iraq to enable the continued fight against the Islamic State militant group that has seized territory in Syria and Iraq.

"The fight against Islamic State has not yet been won. Only together will it be possible to take the next and perhaps most important steps to deal with the challenges to come," he said.

The president of Iraq's ruling Shi'ite coalition told Reuters in April it would oppose a Kurdish referendum.

A senior Kurdish official, Hoshiyar Zebari, told Reuters in April the expected "yes" vote would strengthen the Kurds' hand in talks on self-determination with Baghdad and would not mean automatically declaring independence.

The Kurds play a major role in the U.S.-backed campaign to defeat Islamic State (IS), the ultra-hardline Sunni Islamist group that overran about a third of Iraq three years ago and also controls parts of Syria.