"Such attacks aim to heighten tensions in this particularly sensitive region on Tuz-Khurmatu," Martin Kobler, the U.N. Secretary-General's Special Representative for Iraq, said in a statement.
The attacks by two suicide bombers took place around midday Tuesday as Shiite Turkomans rallied in the city, a local police source told China's Xinhua News Agency on condition of anonymity.
The bombers wore explosive vests.
One set off his explosives inside a tent at the rally. The second suicide bomber set his vest off as police and demonstrators rushed to help and evacuate the victims of the first blast, Xinhua reported.
Among the injured were Turkomen leaders Ahmed Abdel-Wahed and Ali Hashem Mukhtar, the U.N. statement said.
The Shiite Turkomans were rallying to call for the formation of a special force in Tuz-Khurmato to protect them from al-Qaida militants, Xinhua said.
Kobler urged Iraqi leaders to ensure all communities are protected.