Five bombs exploded at a northern Iraqi oil field on Saturday morning, damaging two pipelines without affecting the country's vital crude exports, officials said.

The pipelines transport oil from the Bai Hassan field in the disputed province of Kirkuk to the Ceyhan pipeline that exports crude via Turkey.

"There was an explosion against oil pipelines in the Bai Hassan oil field; it was a terrorist attack," said Abid Hassan, mayor of the Dibis district where the field is located.

An executive of state-owned North Oil Co said two bombs struck the pipelines at around 6:30 am (0330 GMT), which damaged the pipelines but "has not affected the export of oil".

Three other roadside bombs detonated at the field, but did not cause any damage, and security forces defused two more.

"There is no protection for this oil field from the oil and security ministries," the executive said, referring to the interior and defence ministries. "They depend on tribes who live nearby to protect them, but these tribes do not have arms."

Oil ministry spokesman Assem Jihad was not immediately available for comment.

The Bai Hassan field lies within a tract of disputed territory that is claimed by both the central government and Kurdish regional authorities. The unresolved row is frequently cited by diplomats and officials as one of the biggest threats to Iraq's long-term stability.

The Kirkuk-Ceyhan pipeline pumps between 450,000 to 500,000 barrels of crude oil per day.

Iraq relies on oil sales for the vast majority of government income, and of its approximately 2.45 million bpd of exports, most are via terminals in the south of the country.