* Car, suicide bombs explode at PUK headquarters
* Sunni militants claim responsibility
* Latest in string of militant attacks across Iraq (Adds analyst comment)
BAQUBA, Iraq, June 8 (Reuters) - At least 18 people were killed in two blasts at the headquarters of a Kurdish political party in Iraq's ethnically mixed province of Diyala on Sunday, local officials and medics said.
Most of the victims of Sunday's attack were members of the Kurdish security forces who were guarding the office of the Patriotic Union of Kurdistan (PUK) party in the town of Jalawla, 115 km (70 miles) northeast of Baghdad.
"A suicide bomber parked a car packed with explosives near the PUK headquarters and after it went off, he managed to sneak into the building and detonate his vest," said Khorsheed Ahmed, chairman of Jalawla city council.
The explosions were the latest in a formidable show of strength by militants who in recent days have overrun parts of two major cities, occupied a university campus in western Iraq and set off a dozen car bombs in Baghdad.
Jalawla lies in disputed territory, and is one of several towns where Iraqi troops and Kurdish peshmerga regional guards have previously faced off against each other, asserting their competing claims over the area.
Both are a target for Sunni Islamist insurgents who have been regaining ground and momentum in Iraq over the past year.
The Sunni militant Islamic State in Iraq and the Levant (ISIL) claimed responsibility for Sunday's attack in a statement posted on its "Diyala Emirate" Twitter account, and said it was in revenge for the arrest of Muslim women in Kurdistan.
"HIT AND RUN"
ISIL gave a slightly different version of the attack, which it said had been carried out by two suicide bombers, the first of whom drove a car packed with explosives into the PUK's compound and blew himself and the vehicle up.
The second, whose name indicated he was a Kurd, then entered a crowd of people that had gathered to help those wounded in the first blast and detonated his explosives belt amongst them.
In April, a suicide bomber struck a Kurdish political rally in the town of Khaniqin, also in Diyala, killing 30 people.
Nearly 800 people were killed across the country in May alone - the highest monthly toll this year so far - and last year was Iraq's deadliest since violence began to ease from a peak in 2006-07.
Baghdad-based political analyst Ahmed Younis said ISIL was benefiting from the group's consolidation across the border in Syria, which allowed it to focus on Iraq and drain the army's resolve and resources.
"Hit and run attacks conducted by ISIL in Iraq, especially in the mainly Sunni provinces, keep the army engaged on multiple fronts and definitely draw the government forces into a protracted battle," Younis said.
Police and security sources said Iraqi special forces were still fighting on Sunday to regain control over several districts on the left bank of the river that cuts through the northern city of Mosul, which militants moved into on Friday.
Two members of the Iraqi elite forces were killed in clashes there on Sunday, the sources said.
In the western province of Anbar, militants withdrew from a university they occupied on Saturday and took up positions in the surrounding area, shooting at the army as they tried to enter the campus, according to police, security officials and witnesses. (Reporting by Reuters stringer in Diyala and Ahmed Rasheed; Additional reporting by Ziad al-Sinjary in Mosul and Kamal Naama in Ramadi; Writing by Isabel Coles; Editing by Sophie Hares)