Iraq's Kurdish region has claimed disputed northern oilfields in another blow to efforts to forge a united front against the Islamic State group-led rebellion, as twin bombings killed 31 people.

The regional Kurdish government further raised the stakes on Friday by claiming control over disputed northern oilfields.

"Production at the new fields under (Kurdish) control will be used primarily to fill the shortage of refined products in the domestic market," it said, adding that staff from the federal North Oil Company could either cooperate with new management or leave.

The move enraged the federal government, which labelled it "irresponsible behaviour which violates the constitution and the national wealth, and disregards the federal authorities and threatens national unity."

The oilfield takeovers come after Kurdish Peshmerga fighters moved into stretches of disputed northern areas vacated by Iraqi forces during the initial Islamic State offensive last month, and regional president Massud Barzani has said they will stay there.

Security challenges

But in a sign of the major security challenges Kurdish forces face, a suicide bombing followed by a roadside bomb blast at the entrance to Kirkuk city, the province's capital, killed at least 31 people and wounded 25 on Friday, health official Sabah Mohammad Amin said.

Many of those killed were people who had fled fighting in neighbouring provinces and were trying to reach safer areas in southern Iraq, a senior security official said.

Al Jazeera's Zeina Khodr, reporting from the northern Iraqi city of Tuz Kharmato, said the Kurds were facing both "enemies on the ground and enemies with the central government in Baghdad".

"The Kurds now share up to 1,000km of border with Sunni groups and no group has claimed responsibility (for the bombings)," Khodr said.

"Territory is being fought over by Kurds, Sunnis and Shias, the country is now divided into Kurd, Shia and Sunni provinces. But here south of Kirkuk, the lines aren't clear." 

Kurdish Peshmerga forces moved into the disputed northern oil city of Kirkuk in June, shortly after Iraqi government forces fled in the face of an offensive by Islamic State group fighters.

Iraqi Prime Minister Nouri al-Maliki has accused the Kurds of exploiting the security crisis to push for statehood.

Iraqi forces also on Saturday beat back a fresh assault by Sunni fighters on the town of Haditha, which is strategic for its large dam and oil refinery.

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Source: Al Jazeera and agencies