BAGHDAD, (Reuters) – An unidentified Iraqi security forces unit raided a provincial governor’s office early on Tuesday, killing the governor’s secretary and clashing with other units in one of the most volatile parts of Iraq.

Diyala province’s Governor Raad Rasheed Mulla Jawad, who survived a bomb attack last week, said a counter-terrorism unit had stormed his office at 2:30 a.m. (1230 GMT), killed secretary Abbas Ali Hmoud and arrested a member of the provincial council. “The body of the martyr will stay in the building until the killers are captured,” the governor told Reuters. The governor was not present in the building during the raid.

It was not immediately clear who was behind the raid, which comes at a time of mounting political turmoil in one of the country’s most violent provinces.

The men who conducted the raid arrived in military vehicles and wore uniforms but were not otherwise identifiable.

A U.S. military spokesman said: “The operation on the Diyala governance centre early this morning was done without the knowledge or assistance of coalition forces.” He said an American helicopter was nearby but did not fire.

After the force left the governor’s office it clashed with Iraqi army and police units in the provincial capital Baquba.

A source at the governor’s office said four policemen and two civilians were wounded in the fighting before the raiding force withdrew.

Diyala, an ethnically and religiously mixed province in a fertile area north of Baghdad, has remained one of the most violent parts of Iraq even as the rest of the country has become safer over the past year.

U.S.-backed Iraqi forces launched a crackdown last month on Sunni Arab militants believed to be hiding out in its lush palm groves. The Americans and their Iraqi allies have also battled what they say are militias that have infiltrated the police.

The province appears to be entering a period of turmoil involving a conflict between provincial authorities and an ousted police chief.

The governor survived a bomb blast on his convoy last week, days after the provincial council voted to fire the police chief. The issue has led to street demonstrations. The provincial council announced it was suspending its meetings until it received an explanation for Tuesday’s assault.

The governor called for a three-day period of mourning for his dead secretary.