A suicide attack using an armoured vehicle packed with explosives against an Iraqi police base northwest of Baghdad killed at least 37 people on Monday, officers said.
They said the attack was against a federal police base between Samarra and the Tharthar lake.
A doctor said the bodies of at least 37 people were brought to Samarra hospital. "They are mostly policemen," he told AFP.
He said at least 33 people were also wounded in the attack, which some police officers said was carried out with a tank.
The area is being used in a military operation aimed at cutting off the Islamic State jihadist group's supply lines in Anbar province of western Iraq.
IS fighters have over the past year seized a formidable arsenal of military vehicles, weapons and ammunition from retreating Iraqi forces.
"The attack was carried out with a tank and left more than 70 killed and wounded," a senior police officer for Salaheddin province said.
Iraqi security forces have in recent days successfully repelled several suicide attacks involving explosives-laden vehicles thanks to guided anti-tank systems.