A series of bombings has rocked Irbil, the capital of Iraq's autonomous province of Kurdistan, killing six members of the security services.
Irbil is in a stable part of Iraq and the region has not witnessed such attacks in the past six years.
A central government spokesman said the violence could be linked to fighting between jihadists and Kurd in Syria.
Meanwhile, at least 25 people were killed when a suicide bomber attacked a Shia Muslim mosque south of Baghdad.
The blast is reported to have brought down the roof of the mosque in Mussayab, and bodies are feared to be trapped in the debris.
The attack took place as a funeral was under way for a man killed by militants a day earlier, said Reuters news agency.
Sectarian violence has surged across Iraq in recent months, reaching its highest level since 2008.
Both Sunni and Shia places of worship have been targeted in recent months.
At least 36 people were reported wounded in Sunday's bombings in Irbil, which targeted the security forces HQ and the interior ministry.
Reports described a car bomber who rammed a checkpoint leading to a complex housing the interior ministry and a number of security agencies.
A short while later - as emergency services arrived - another bomber struck driving an explosive-rigged ambulance, and gunmen on foot also attacked.
TV images showed black smoke rising high above the city and emergency vehicles racing to the scene, which was sealed off by security services.
"We were inside the building when there was a huge explosion outside, and when we tried to go out to see what happened it was crowded, and there was shouting everywhere," said Farhan Samed Kamil, an asayesh member who lost two fingers in the attack.
"After a while there was a second explosion. That's all I remember," he told AFP news agency from hospital.
A statement reportedly published on the Kurdistan Regional Government (KRG) website cited witnesses as saying five would-be suicide bombers had been killed before they were able to blow themselves up. Other official reports suggested four militants had been killed.
Nozad Hadi, the governor of Irbil province, told AFP news agency that the victims were members of the Kurdish "asayesh" security services.
The region does not usually experience the violence common elsewhere in the country.
A spokesman for Iraqi Prime Minister Nouri Maliki was quoted as saying the attacks could be linked to fighting between jihadists and Kurds across the border in Syria.
That view was echoed by Iraqi security analyst Ali al-Haidari who told AFP news agency the attack was "al-Nusra Front's revenge against the Kurds inside Kurdistan".
The conflict in neighbouring Syria has caused thousands of Syrian Kurdish refugees to flee across the border into northern Iraq.
The blasts come a day after results were announced in the region's parliamentary elections.
The main opposition Gorran (Change) party moved into second place, ahead of President Jalal Talabani's party.
His Patriotic Union of Kurdistan (PUK) had shared power in the previous government with the Kurdistan Democratic Party (KDP), which won most votes in the latest election.